Another question: I'm thinking about upgrading to a new computer (current machine gets 4300 on benchmark medium settings, but it's three years old and getting slow). The new machine I'm looking at comes with NVIDIA Geforce GT (Not GTX) 620. How does the GT 620 compare to the GTX 5xx Square recommends?
It's a terrible card...typically with pc parts, you get what you pay for. There's a few exceptions like the intel extreme processors which are usually not even close to the worth of their price tag. I know it can suck as a student, or with a tight budget, but I highly recommend spending a touch more up front so in a year or two you're not already behind and forking out more money. Save over longer if you have to. I bought a used q9550 a few years back, little pricey...but still going and I'm ok to wait at least another year before upgrading my setup. Same goes for ram, mobo, case, psu, etc. You spend a bit more up front, your psu can be good for years along with a case.
High end can last you 6-7 years sometimes, where as going for lower end, you'll want new in a year or two. So instead of spending that 900$ in one shot, you spent 1200$ over a few years. So if you have a capable machine in your possession save up and get some good parts.