Open exhaust, low end, 1/4 mile times

I've always been told that on a mild engine like mine that cutouts are a waste and will only loss bottom and anything on top that I would gain I wouldn't notice. At the track today I ran 6 runs with exhaust on and got a best of 12.98 @109.25 with a 2.12 60'. Ran 6 more with the cutouts open and ran a best of 12.76@ 111.31 with a 2.07 60'. Almost all my 60' with the exhaust open were faster than with it closed. That's 2 mph more on the top end too. I think the cut outs were well worth it. Am I not losing any bottom end because my cutouts are 2.5 inch and not 3 inch? Most everyone seems to say that 3 inch is way too big for a 351 with about 350 horses at the engine but it seems like 2.5 inch is holding me back.

Yes, tires are going to do me best. Cutouts are only $40 though. I'm worried about my stock tranny with some sticky tires. I've been told by multiple transmissions shops that my engine alone will blow the tranny. I've got about 80 1/4 mile runs on it with no problems yet. I'm graduating in a month with no job lined up so money is short right now. I'm a criminal justice major if anyone knows of some openings.