This site has the benchmarks you're looking for. Anandtech also has excellent reviews. The Anandtech reviews show a deeper understanding of computer technology. I prefer their reviews and bench tool. You can use their bench tool to directly compare any two chips.
You haven't given us quite enough information. WHICH Phenom II X4 chip are you talking about? I'm going to assume the 955 for this comparison.http://www.anandtech.com/bench/Product/109?vs=88
The i5 750 is certainly the faster chip, but it's up to YOU to decide if it's worth the extra $100. If I, personally, had to choose between those two chips I would pick the i5 750. The problem is that I don't really game on my systems. I do more video editing than gaming so the i5 is the easy choice between those two chips for me.