Like Barbara I know of an installation where a Canon 8300 serves as a room divider in a 2 room bachelor apartment, and the space is better for it. There are even some Home Depot ferns snuggled up against it. You don't need to get behind it, so you can also push it up against a wall. Other than that, it is bit on the huge side. For almost 3 years now mine has worked perfectly in a space that fluctuates between 20% humidity (winter) and 70% humidity (evaporative cooled summer), and a wide range of temperatures. It is also rained on by flakes of Gatorfoam particles and an occasional dusting of varnish overspray. And it's quite close to a kitchen. No matter, it's perfectly happy and seems insensitive to such things.
You should have no trouble getting 40 x 60 inch prints from your D800. On the condition that your originals are very sharply focused and properly exposed. For most types of media anything above about 180 camera pixels per inch of print will give you a sharp looking print if your original is sharp, and you do reasonable post processing so as to not lose what you start with. With careful upsizing, it gets even better. If you want dazzlingly sharp prints, you can shoot stitched panoramas where you join together several side my side images (in Photoshop for example) to get a single high resolution image. It's not hard to 1/2+ gigapixel images that way. Two row, camera-vertical stitches with a D800 yield 300 camera pixels per inch of print at over 40 inches high, and those prints simply blow people away with the detail, assuming the right type of subject and presentation.
The one BIG THING about large printers is that unless you use them fairly often, you face the possibility of exquisitely annoying nozzle clogs that will degrade your prints. There are a few posts on LuLa about that, ahem. The 8300 is better than the Epsons in that respect, although that is just one of many issues that differentiate those and other printers. For instance, the 8300 doesn't handle sheets as well as the Epsons, it's much more roll-oriented.
Unfortunately, you are coming into this at a time when there are no big promotional printer sales going on. Usually, towards the end of the year the manufacturers give heavy discounts (I bought my 8300 for $2195), and sometimes at other parts the year. But we didn't see that in 2013. Could be those days gone, dunno. But you can talk to the sales people at various suppliers for heads-up tips on when those sales might pop up.
