Buying new hardware for SVP advice.

Hey guys, I'm currently running an e4600 2.4 ghz dual core processor with 4gb ram and a geforce 8600gt and getting quite poor results with SVP. I can watch small video files with high cpu usage but 720p videos are unwatchable. My aim is to be able to watch 720p video lag and artifact free and I know that this will require a new processor. However, since my motherboard is old, If I was to get a quad core processor, say an i5 for example, I would need to buy a new motherboard and ram etc. So what I'm thinking of doing is buying a better dual core processor, namely a Intel Core™ i3-3240 Processor 3.40 ghz.

My question is, how well would SVP run if I used my current set up with the i3 processor? What would be the difference between that and the i5? Would both of them be able to play 720p video well?

Thanks very much