Before I installed the heads I installed the 3.73s with the stock 5.0. Everywhere I read said that the gears would lower my ETs. NOPE!!! The stang didn't get any quicker with the stock setup and new gears. Sure, the car was plenty fun to drive but did not get quicker in the 1/4 mile. I believe Slow5.0 experienced this as well before the H/C/I upgrades. Now you have ported stock heads/intake and a cam so you have moved your horsepower peak up a bit in the RPM band. So, gears may help you a little. But, I would consentrate on your 60' times and get some drag struts/shocks and/or drag springs. Are you running street tires? If so, get some drag radials. Looking back I would have waited on gears for a little longer.
4.10s @ 75mph with stock T5 will run 2500-2700rpm.
3.73s @ 75mph is just under 2500rpm.