Core i5 750 is faster than core 2 quad Q9550
9800 GT is faster than HD 4670, but the HD 4850 is faster than 9800 GT for about the same price (or maybe cheaper).
What do you want to do with that computer?
If you are gaming then q9550 with 9800 gt will certainly do better most of the time, if you are into cpu bound workloads (encoding, rendering) then the core i5 is certainly faster than the core 2 quad.