It has only 1 pci-e 2.0 buss slot running at x16 there is no chance to bottleneck.
P43 is not powerful enough to handle high traffic the x48 chipset is mutch faster but hard to find, i suggest for you to go for a P45 or if you can afford P55 mothebords are better.
Eh? OP is only using one card, so he/she only needs one PCI-E lane 2.0 x16, which the motherboard he/she linked too has. A P55 mobo is for 1156 CPU's, not s775 CPU's.