X58 motherboard and GTX285s Only negotiating to PCIe1.1

Here are my Results with SKD BandwidthTest.exe:

BUS PCIe2.0 x16
VGA Card = NVIDIA 9800GTX+
CPU = Intel Core i7 920 (Quadcore with 2,8GHz)
Memory = DDR3 1600MHz Tripple Channel Memory
operation system = Windows XP 32Bit

Memcopy from PC to GPU = 5200MByte/second
Memcopy from GPU to PC = 4700MByte/second

Is a 64Bit operation System (Vista 64Bit) better as a Windows XP 32Bit?
Get I more bandwidth with a NVIDIA 285GTX?