pci-e x4 slowdown? cpu upgrade

Hi, currently i have a 8500gt ( terrible card ) and im looking for an upgrade most likely a 9800gt(http://www.pricespy.com.au/pno_13544.html) or 8800gt(http://www.pricespy.com.au/pno_11782.html)
and would the 9800gt be faster for that extra 4 bucks
but i have the problem that my pci-e slot is restricted to x4 unlike the normal x16 or 2.0 i also know that a x8 will not make a diffrence but is the restricted x4 slot going to make a diffrence.
im also going upgrade to a c2d e4600 (mobo is restricted to 800mhz fsb) if that helps from my current pentium D 915.
help appreciated
:major:major:major