Like he mentioned, if he's on a budget than I don't see a reason to save some money on something as minor as 32 bit vs 64 bit. 4GB of RAM is still plenty fast enough, a 550 Ti is a mid-end card, it's not going to be hampered by not having 32GB of RAM
. As for programs that uses 64 bit, nate167 said he only plays flight sims, and pretty much every flight sim I know runs on 32 bit systems (yes, including DCS: A10, which I have).
It's building what he needs, not what you need.
That's the best combo of cheap and performance (I would change the GPU, but he's getting one for free) that I could think of.