21 inch iMac video card enough?

The hard thing about this list is that it doesn't tell you how it performs on the bigger screen.  I'm sure the extra resolution of the 27" is going to bog the video card down more than if you were to run it on a smaller screen.  Basically, even though the base 27" iMac has a slightly better video card than the upper end 21.5" iMac, is it really going to run better at all due to the higher resolution?  For the money, I'd rather max everything else out on the 21.5" than to have i5 and no fusion drive with a bigger screen.

Not trying to argue, just trying to learn.  If it really is a big leap to get a better video card, by all means, enlighten me.