I've had Epson printers for years. The last 24" was a 7000, and I still own a 4000. I was nervous about jumping to Canon, but am extremely pleased with iPF6100 I bought last summer. At this point, the 4000 is gathering dust, the 7000 is up for sale (I'd used it exclusively with the Cone Piezography inks, for which is was excellent). The Canon has been problem free and frugal in its use of inks. Other than the Photo Gray and Gray inks (I do a lot of B&W printing), I'm still working with the original starter ink carts. Remember that while the new 7900 may take 700ml carts, those cart ARE NOT CHEAP. For the Canon alone, an entire set of 12 130ml ink carts is close to $950. For the Epson, a complete set of 11 carts costs: 150ml=$990, 350ml=$1760, 700ml=$3080.
Though the 6100 is "older", the technology isn't changing as rapidly as ink technology. The current ink set produces excellent results, and especially good B&W prints. As a final thought, when it comes to printers, think of razors and razor blades. The printer is almost a loss leader (especially consumer models), and a vehicle for selling ink. I'd chose the model that seems most frugal when it comes to ink, all othe factors being equal. At the moment, that seems to be Canon.