Wondering which computer to buy of the 3 options I'm considering

Hi Everyone: any and all advice welcome. I am on a budget and wondering of the three system options below, which would be a mid level + better gaming system. Bear in mind that in either case, I will add more Ram and an upgraded Video card in any system option. I’m leaning towards the older GX745 because of the price and thinking it may perform close to the new low end computer options listed. Am I right? Ready to buy so any suggestions ASAP.

A) $150.00 for an older Dell Optiplex GX745 Tower, Intel Dual Core 3.4GHz, 2GB DDR2, 160GB HDD, DVD/CD-RW. 800MHz Bus Speed & 4MB Cache. Basically, (2) Pendium 4’s (925). OR B) $299.00 The new and more expensive Dell Vostro 260 Mini Tower Pentium Dual Core, Genuine Windows® 7 Home Premium, 2GB memory, 250GB HDD Intel® Pentium® processor G630(2.70GHz, 3MB) OR C) $369.00 Dell OptiPlex 390 Desktop Intel® Pentium® Dual Core G630 Processor (2.7GHz, 3M) comes with a limited 3 year warranty if I buy through business. So may be better than option 2 for the strong warranty.