As long as you've got the res. it's all good. I use 2x 24 inch monitors; 48inch at 3840px width and the pic is sharp at around 2FT. That said, your not really concentrating on a 48inch screen, rather a 24 inch one; ignoring the other. The dot pitch is slightly larger than the 27inch imac but I prefer it tbh.
I'm going to wait for the 4k TV's to come down before getting rid of the 40W5500... could be a bit of a wait though, lol.