This is what I was thinking.

A lot of nice flat bar bikes have been suggested, but none of them strike me as something that would be a lot faster than a Scott SUB. I'm just not sure switching to another flat bar road bike is going to make much difference. Get some Mavic Aksiums on eBay and a set of GP 4 Season tires. If you still aren't satisfied, try a tighter cassette or maybe a new crank.