The first thing i'd do is buy a cheap 500GB 2.5" sata SSD (or even 1TB if your image is larger), clone your existent hard drive image, and copy it to the SSD. This alone will make your system feel 10 times faster.
As far as the CPUs go: 4770, 4770k, 4790, 4790k or 5775c depending on whether your motherboard BIOS supports the latter three CPUs. Tthe first two should be supported by the BIOS that supports 4130. I'd check your power supply specs - if it is weak, it will cause instability issues. If the BIOS supports all of the above, I recommend 4790 or 4790k (again, your power supply should be at least 200w). 4790k is about $200 used, but is good to go for the next couple of years. Keep in mind that this advice assumes that you MUST keep your existent system. $350 gets you new motherboard, CPU and RAM. The problem is your system is OEM, so you'd need a new case, power supply, and operating system.