An older revision is faster because it doesn't properly emulate some parts, and is full of bugs. If you run into one of said bugs, you won't get any support in the forums besides use a newer version.
An i5-4670K and a z87 motherboard will cost you about $350. You can probably reuse your case, power supply, RAM (if its DDR3), hard drive, fans, and GPU. You might want to get a new cooler (about an extra $40-60 depending on how good it is).
An i3-4340 and a h81 motherboard will also be vastly superior to what you have, and cost about $200, again reusing everything you can.
An i5-4670K and a z87 motherboard will cost you about $350. You can probably reuse your case, power supply, RAM (if its DDR3), hard drive, fans, and GPU. You might want to get a new cooler (about an extra $40-60 depending on how good it is).
An i3-4340 and a h81 motherboard will also be vastly superior to what you have, and cost about $200, again reusing everything you can.