Going from 2.73's to 3.55's is a nice leap, but for the little bit of difference I'd go to the 3.73's.
I'm running 4.10's behind a 5-speed in my Vortech-equipped Cobra. The blower really doesn't do anything under normal driving conditions. I find with the lower rear gear I can run the tranny in a higher gear, except of course 5-th is the limit. But I can cruise in bumper-to bumper 25-MPH rush hour traffic in 5-th without lugging the engine. So, if you think your giving up gas mileage you can compensate with a higher gear selection in the tranny. Of course for out-and-out performance, the higher-numbered rear gear ratio will accelerate more quickly at the expense of lower mileage. But hey - it's a kickin the pants. Do the 3.73's, hang-on and pay for the gas!