At 1920x1080 resolution, a 1GB model will do a much better job than 768MB. Also the SE 1GB is the low-end version with 288 shaders (vs. 336) and even lower performance than the 768MB version. If the budget were less than $200, that would make sense to consider a more budget-friendly, lower-performing model, but I think the idea is the get the most performance without going over budget.
Quote:
"I have to admit I'm quite disapointed by what the GeForce GTX 460 SE delivers. In most of our benchmarks we see the card trailing well behind the GeForce GTX 460 768 MB - about 7%. When compared to the 1 GB GTX 460 the difference is even 15%. Unfortunately the reduction in performance has not resulted in a significant decrease in power consumption. The card basically consumes just as much power as the GTX 460 1 GB and 768 MB."
http://www.techpowerup.com/reviews/Gainward/GeForce_GTX_460_SE/