Well, my roadie has 700's. I bought my road bike simply because I loved it and it felt fast. Nothing scientific there.

My tri bike has 650's. I bought my tri bike because they were closing out new Cervelo's for $500. It was bought over the internet and I never test rode it... nothing scientific there.

In the end... I truly believe that a 650/700 wheel isn't going to make a huge difference... the engine running the bike does.

I ride a very nice road bike (Specialized Tarmac Expert- full carbon/full Ultegra)... but people on less expensive bikes fly by me all day long.

I say go for the bike that fits you the best and you love to ride... and whatever wheel comes on it... go for it.