Gigabyte 1GB 460 here. Lovely card; cool as a breeze (runs as hot under load as my old card in idle), easy on the PSU and scores high on performance. Quiet too, thanks too the custom cooler. Factory OC without price increase (yay Gigabyte) and can go a lot further with little effort. Quite a nice step up from an G92 8800GTS.
I say go with the 1GB model. There's more difference than just the amount of memory: the 768MB model has more of the core disabled. It's more like a GTX455 than a 460.