I would not necessarily buy an SP4900 at this time. My experience is that unless it's used at a maximum interval of every third day it will show missing lines in the nozzle check and need cleaning. I've had mine for over 5 years and the print head remains fine - for about 3500 sq. ft. of output over the period - low by commercial usage standards as I am not a commercial printer. Print quality remains really very good; but the new models from both Epson and Canon deliver somewhat better Blacks, and according to Epson the reformulation of the yellow ink for the new SureColor series would make SC800 yellows more fade-resistant than for previous models.
If you don't need more than a 17 inch carriage - and you do not intend to print with either rolls or posterboard (or the like), then the Canon Pro-1000 is an excellent choice. The paper feeds are fast and easy, no ink-switchng between matte and photo Black and the print quality is superb. If you intend to make panos or to feed posterboard into such a printer, then you would need an Epson P800 because it can take a roll holder (optional accessory) and it has a slot for flat-feeding very heavy media that the Canon does not. The feeding mechanism for fine art media is not as user-friendly or fail-safe as Canon's, but it's workable. As for cost of ink between these two models, we won't know because there isn't enough basic data made available to measure it. For Epson there is none whatsoever. The Canon has a utility that provides an excellent track on ink used for prints, but not on whatever amounts it uses internally for keeping itself clean - and it could be significant, but we don't and won't know.
Getting into the 24 inch models, as I have not tested an Epson SC7000 yet, I cannot provide any first-hand advice on it. I've seen it at trade shows, really nice looking printer and the output looks great, but I have no feel for the fine points. I have been working quite a bit with the Canon Pro-2000, and would suggest that if you need that width you can't go wrong. It's a really fine printer. It's footprint is very reasonable for that carriage width because of how they designed the positioning of the ink tanks, so if bulk is a concern, I believe the Pro2000 will be less bulky than an SC7000 - but you can check the dimensions in their spec pages on their websites.