"if I push my wife's desk workspace out to the side yard..."
Sal, I think putting your wife's desk outside would encourage creativity and enhance her productivity-- cold, fresh winter air is good for the mind!
I just went through something similar. I've owned Epsons for a long time and my most recent one was a 7900. I agonized over whether or not to make the switch to Canon and was really worried about giving up image quality in any tiny w ay at all. I did everything I could-- read reviews on the older x300, looked at color gamut comparisons between epson and canon, and specs, and tried to get info on black and white printing. I was concerned that some had mentioned a visible dither pattern on the Canons and didn't know if there was any real world impact from the difference in specs: (epson 2880x1440 and 3.5 picoliter/variable droplet size vs 2400x1400 and 4 picoliter droplet size on the Canon). Also, I was really used to the Epson workflow and quirks and had some profiles made from a couple different people that worked really well. My 7900 was a hassle for me to operate but the results were truly excellent and after everything, I was still super reluctant to move to Canon from Epson.
I ended up getting the 8400, and yes, it's not small. It doesn't fit anywhere except our dining room which is not that large, so now there's a dining room table, upright piano, and gargantuan printer with almost no room to walk through. It's funny that the 6400 is lighter than the 7900 (154lbs vs 187lbs for the epson), but the 8400 is much heavier than the 7900 (316 lbs vs 256 lbs). No doubt-- the 8400 is a commitment in terms of getting it into your house and finding room for it. But I second what Rob said-- if you can get the Canon at a time with max rebates, the 8400 is just too good of a deal to turn down with those 330ml tanks. You don't get that with the 6400 series or with any of the Epsons. You also get the built in hard drive on the 8400 which is on the 6450 but not the 6400.
I'm reluctant to say much about image quality as I've only been printing for about a week and I haven't had much time thus far, but so far, there have been good results out of the box. I have only used the stock profiles from Harman and Hahnemuhle on a few papers. (Harman, Hahnemuhle, and Canson have stock profiles for the x400 canons on their websites while the other papers I checked do not.) I've printed the most on Harman Baryta Gloss. Caveats aside, out out of the box, the prints look great and will only get better as I get profiles made from a couple people, have time to experiment, and also try out True Black and White. It's not that they look identical to my epson 7900 prints- they don't. But the differences are not in a way where one is superior than the other across all types of shots; you have to examine closely and stare at different areas of the print. There are prints where I subtly prefer the epson, but it's also an unfair comparison as I had the epson 7900 for a couple years and had experimented quite a bit with different profiles as well as trying to make my own. I've been trying to print shots to find the Canon's weakness (lighter reds/oranges very detailed/textured shots that might show the dither pattern). I do think the Epson has a finer and fairly remarkably detailed dither pattern, but I've been looking at prints with a 4x and 8x loupe which I know might seem excessive. I'm funny that way though and I like to understand what's on the paper. I also think sometimes a print can give someone a stronger guttural reaction in a way they can't articulate and sometimes examining the details closely can shed light on those overall impressions. Hopefully over the next month, I'll get profiles made and have time to experiment and have a better understanding of the differences between the two printers.
It's worth mentioning that operationally, the Canon has been a joy and a revelation thus far. I never thought that organizing matte and glossy prints in batches was that much hassle with the epson, but it's amazing how nice it's been to not have to run cleaning cycles, switch between inks, etc. I was always aware of how much ink was being wasted on my Epson. Run a print check, run a cleaning cycle, switch from PK to MK and then after it's switched, when you go to print, it runs another cleaning inevitably. I didn't think I'd care about the operational efficiency of the Canons. I was quite used to the Epson process and I viewed ink wasting and extra steps and time as part of the process and all I wanted was the best prints I could make.
So take it all with a grain of salt after owning it for only one week, but the Canon 8400 has been awesome to run. You just print. Matte or gloss, different materials, fabrics, etc. You don't worry that you'll come out with banding because the print heads need a cleaning. At highest quality, the Canon is quite fast-- I guess that is one of the differences in the x400 Canons vs the x300 series. It takes about two minutes to power on, but after that, there is much less time when the printer is sort of "thinking"/getting ready to print or cleaning.
Btw, the Canon 6400s have two paths for sheet feed and the 8400s only have one. I had read some people really don't like it, but after the first few times, I've had no problems at all, even with smaller sheets. I think the Epson sheet feed in theory is better, but I have ruined a lot of 8.5 x 11 test sheets with any curl at all on the epson (larger sheets don't have that problem). I print more letter-sized than most people as sometimes I just like to run off a small print and look at it for a while before I print something large. There are a few quirks on the Canon (I can't print from the Canon driver on letter size without hitting preview first-- otherwise, it says I can't print because the dimensions are wrong). But now that I have the process down, sheet loading is no problem.
It will take a month or two to get some profiles made and experiment more. Don't know if this is helpful for you, but basically the first week with the Canon 8400 has been really good both operationally and in terms of image quality. If you can get a good deal on the 8400, it's worth making the room for from a value perspective. If you have any specific questions, I'll try to answer along with the other canon owners here. Good luck!