I just put together a budget rig.
Asus P5K Pro- 110
e5200 CPU- 85
HD4670- 80
Antec 300 Case -50
Antec Earthwatts 500 Watt PSU- 50
2 Gigs pc6400 w/ heatsink- 30
Freezer7 Pro- 30
435 + shipping
The CPU overclocks from 2.5 ghz to 3.5 with stock cooling. I'm @ 4ghz stable, 55 degrees under load with the freezer 7 and antec300 case. The mobo leaves me upgrade options when needed. Very happy with it.
The starter of the thread stated a good gamer, upgradeable and use for a few years. IMHO the system you speced out does not meet the requests. The specs of the system your stating most likely will score between 4 and 7k on 3DMark06. Not a gaming system at all. You say that the MB has room for upgrade, none of the other components do, so your out repurchasing Video card, Power supply, memory again rather then adding a video card or additional memory.
The PSU is crap I won't even sell an earthwatts psu. I think the max amps on one of the rails is 22 forget any good video cards or a crossfire comfiguration, It has a max of 4 SATA connectors, you CANNOT use a 260 or 280 video card. and I dont think it has the power for a 9800. The MB is for Crossfire upgrade, the PSU wont handle it. PC6400 is SLOOOOOOOOW memory and it will be hard to get to a decient FSB without way overvolting it. The processor does overclock well but, with the memory stated you will never be able to use the overclock since your FSB will not be able to compete with the processor speed maybe get that memory at best to 1066. What voltages are you pushing your processor at? Anything over 1.325 your risking frying your processor, all the OC specs I have seen over 3.8 on that processor are at 1.35+.
Overclocking a rig for gaming is not a question of "what I can push my processor to" alone, its FSB, Memory timings and their relation to the FSB, not to create bottle necks which actually slows system performance. Its to have all components work in harmony to produce a fast and stable rig. Heck I have a liquid nitrogen pot for processors and gpu's, I can get 22GHz out of some processors and more on others but that does not make the system fast. I guess I live in a different world when it comes to gaming systems, I build out for Industry Standard scores (3DMark06) not what I can get for the cheapest price and Overclock and say my system runs at _____. When my reputation as a builder, supplier and world ranked overclocker is on the line, I do not compromise quality for price.