Upgrading to e8xxx, i5, or i3

I'm planning on upgrading my 3 year old desktop, more or less, just my CPU.

I currently have an ancient e6300 running at 2.01Ghz, on an unknown ECS 570i motherboard, which explains the lack of overclocking ability. 2Gb of DDR2 667 RAM and a 8800GT GPU.

I think my GPU is fine, not worth upgrading in my price range yet, but I know I need a new CPU. I use my PC mostly for gaming, but also interested in getting a BD player/burner and a 1900x1080/1200 monitor, up from my 1440x900. I also use CAD occasionally and rarely some video editing. Plus casual music and internet.

Elaborating on the gaming, I don't just play old RPG's, I like to run the best-looking at the highest settings I can. So keep that in mind.

Anyway, I had been looking at the e8400 for $170 at Newegg, but the new i7 and i5's are cheap quad-core options. Not so much the i7, because they're above my price range, but the i5-750 is $200 at the same place. But there's also the dual-core i5's, which is $195 for the i5-650 also at NE. And on top of that, the i3's are suppose to be cheap and very "over-clockable".

I don't have a problem overclocking, I've done a bit of it, but I'm not going to go hardcore. I have a crappy case that I'm replacing with a 900-2, which will help keeping things cool, in addition with an aftermarket heat sink and all that. I believe ineffective cooling and airflow had a big role in my inability to overclock much. With that said, what CPU would be best for my uses and price range of up to $200 or a little over: e8400, i5-750, i5-6x0, an i3-5x0? Can be something else similar, but has to be Intel. I guess I'm a fan boy  

Also, suggest a motherboard for the CPU, price limit: $150. Preferably, on Newegg. Thnx in advance.