the only reason to ever install 32bit is if you have a very rare program that won't run on 64 bit, or some other odd circumstance. Normally this applied to corporate setups and business/professional programs.
You should obviously use 64 bit as you have over 3GB of ram.
The only reason to run 32bit is if you have 16bit programs you run(won't work in 64bit windows) or really old hardware with only 32bit drivers and no newer
64bit drivers. A 32bit os sets a hard limit of 4GB on all memory that can be addressed in the system, including system ram, video ram, drive caches, the
flash ram on the mobo, and more. Normally, 4GB is limited to 3.25, before that gets eaten away by large amounts of graphics ram. In 32 bit, you will have
less than 2GB or your 8 to work with since your gtx670 alone will eat into your 4GB allowance by 2GB. Microsoft imposes a limit of 16GB system ram on
home premium and below, but will let you install up to 128GB of system ram on more expensive versions like ultimate. I believe any 64bit version of
windows allows a virtually unlimited amount of graphics ram above and beyond your system ram. We probably won't hit the memory address limit of 64bit
windows for a few decades. If you play modern games and either run other programs at the same time(multi tasking) or just leave a bunch of browser tabs
or other programs like media players or chat programs open, you can use all 8GB. Newer versions of windows will also use any available ram you aren't
using to cache frequently used programs and files to make your overall computing experience snappier. If you have a retail copy of windows 7 ultimate
versus an oem copy(which I could fairly guess since you asked which to install, not which to buy), you can partition your hdd and install both. Then you
can boot into whichever one suits your pc usage at any given time. Hope this helps.
jternorj, I don't agree on most of what you wrote.
1. indeed, 16-bit apps are limited in 64-bit (limited, because there are some 32-bit apps that are installed using 16-bit installers)
2. 32-bit windows desktop os is limited to 4GB RAM. Windows Server editions, linuxes, unixes and whatever can use up to 64GB of RAM in 32-bit mode using PAE (check wikipedia). Only apps are CPU-limited to 4GB, and actually 2GB of application data.
3. 64-bit windows requires signed drivers. So developers of drivers have a harder time (think about oveclocking/monitoring tools)
4. having a 3GB GPU (or 2x1GB) will not reduce the RAM availability in 32-bit windows (do you actually have a 2GB GPU under 32-bit windows? or did you just scaled the numbers you read?). I don't know exactly how the rule is, but not all of the VRAM has to be mapped. Through a 512MB window you can access 3GB or VRAM (or more).
5. Not many games have 64-bit executabled. When they do appear, their main advantage will be speed optimizations, not memory usage.
So, to the OP question, for the current games (no 64-bit binaries), there is slight advantage of 64-bit which comes from optimized GPU drivers (but I would say under 5%). For strictly gaming setup, 3GB of RAM is enough until 64-bit games get mainstream. Few game benefit from /3GB switch (which does allow using of 3GB game data), so 2GB for games and 1GB for kernel+cache is enough for the next year. So if you need drivers for old HW (which is buggy or inexistent for 64-bit) or have 16-bit apps/games, stick with 32-bit (although you will not use half of your RAM).