This motherboard supports the latest Intel® Core™2 processors in LGA775 package. It also can support Intel® 45nm Multi-Core CPU. With new Intel® Core™ microarchitecture technology and 1600/1333/1066/800MHz FSB, Intel® Core™2 processor is one of the most powerful and energy efficient CPU in the world
Yes. That P5Q should be able to overclock your e5200 at minimum 3.3 Ghz (1066 FSB) or up to 3.6 Ghz (1200 FSB). I wouldn't change the motherboard. I have 2 P5Q series motherboards that lets me overclock my e8400 to a 2000 Mhz FSB stable enough to run 3dMark06 on the GTX 260. A slightly overclocked e5200 CPU is well balanced with the 4850. Anything much faster and you'll make the 4850 the bottleneck.
You can always sell the e5200 a few months from now and upgrade to the e8000 series as their prices are steadily droppping. But when you do, be sure to upgrade the GPU also to balance out your system's performance.