Okay just throwing this out there, if you play really close to your 46" 1080p tv, games and such are going to look very pixelated. Anyways back onto the topic, i would go with the 2 gigabyte model because I've seen games use more than 1gb of VRAM in modern games at 1080p. I hope that helped you out
No i have seen vanilla skyrim run past 1gig, i have also seen bf3 jump past 1gig at 1080p. So really more modern games do require more vram. So the 2 gig model would still be the one i would recommend. Games like metro 2033 jump past it also.
The amount of memory needed relies solely on the textures the application/game is using, and the resolution being displayed. You can be running at 4k resolution, and playing a game using no textures larger than 640x480 in size and find out that a 512mb card would do the job. Now crank those textures up to 4k res and you will see that the amount of memory needed on that card would sky rocket...and probably bring a 4gb card to its knees.
edit : and as Azathoth said, screen size doesnt matter. 1080p is 1080p. 2 million pixels to control, no matter how you look at it. Only thing that will change is the size of the pixel, the dot pitch, and the amount of power to control the pixels and backlighting.
630 GT 4GB + windows 7 64 bits(32 bits will bottleneck) = best performance for such large screens as 46" and even to 84" ones.
What do you not understand about this? lol THE SIZE OF THE SCREEN MEANS NOTHING ITS THE RESOLUTION! a 46 inch 1920x1080 res tv takes no more vram than a 20 inch 1920x1080 monitor or a 120 inch 1920x1080... I am baffled that you have a veteran status and do not understand that.
If we are looking for a card that will last a while, and 1GB is already becoming a limitation at 1080p in some games(a trend that will only continue if history is any indication), then getting a 2GB card seems like a good idea. The card does need to have a gpu powerful enough to take advantage of it, though.
I'm thinking it would be worth it to spring for a 7850 2GB(you can overclock the snot out of a card like that).