I would like to purchase some new wheels for my two 1/2 Ironmans this summer. I am doing Tupper Lake and Timberman. Right now I am just riding the stock wheels that came with my $600 road bike. Am I going to find any in the $300 or less price range that are decent by using Ebay? Are new wheels going to make a difference over the 56 miles? Should I spend the $300 on just getting a good front wheel? On Ebay, I am finding the following....

Mavic Cosmic Elite - $160

Mavic/Ultegra Road Wheel Set (Mavic Open Pro rims) - $175

Mavic CXP21 black alloy rims with Shimano 2200 - $60

Mavic Ksyrium Elite (2003) - $200

Shimano 105 Matrix 700c - $135

SPINERGY SR-3 700c - $120

Are any of the Performance brand wheels any good?