Please help me fast, want to order today

Hi,i would like to get better performance for FSX.My current hardware is:AMD XP 3700+ (single core) (S939)2gig Dual channel RAMGeForce 6600GT 128mb (AGP)I am not going to change my motherboard, but it has a PCIE and an AGP slot.What would be better for me (only FSX / flying online / addons matters).Should i buy a PCIE grafic card?Or better a nex processor?Processor would be an AMD X2 4400+ (1024kb cache) or AMD X2 4600+ (512kb cache). Both are dual core CPU and cost about 250-280 Euro.If an grafic card would be better for me, please tell me, which one i can use?Cost should not be higher than 280