If you already had the board, RAM and the HD3850 then getting a Q6600 would be the cheapest approach but since you're basically buying everything then it's a no-no. If you still intent to get the 775i65G make sure to get CL2.5 RAM; it's a requirement for Core 2 support. Get an H61 board (socket 1155) and a Celeron Dual Core G500 series. It'll run in circles around your P4. For graphics, even an HD6450 GDDR5 would give you better performance overall, not because the HD6450 GDDR5 is stronger (it isn't, the 3850 is about 3 times faster) but because the P4 bottlenecks the 3850 soo much. H61 board + 4GB DDR3-1333 + Celeron G530 + HD6570 or better would be my recommendation.