Except RAM is dirt cheap anyway, isn't it? And I think 448, like the GTS 320 before it, would be treading the line of a really undesirably RAM handicapped card.
The reason I said 448 is because it's a direct cut-down from the 896MB GTX260 model. As for it being bound by its video memory, you are most likely correct, but we can always hope NV's "fixed" the memory management troubles of G8x/G9x.