Bengel, I can honestly say, I have never heard anybody ever say "gear ratio" is not all that important in drag racing. Personally, I can't think of anything else as important except for tires, in determining how a "stock" car performs in the quarter mile.
I don't know what crowd you hang with, but everybody I know would say, "Yeah, he has a gear" if we were talking about somebody who had a car with 4:11s.
All I can tell you, is I cut 4/10ths off my cars original et. simply by going from a 3:15 gear to 3:54s, and if memory serves, my speed increased also.
I firmly believe that our rather "high" gear ratio is the major reason most every other competing sports car (Z's, RX 8, Boxter to name a few) can beat a Limited XF in a drag race.
It doesn't matter if you're running a Powerglide, C6, C4, 727, or a turbohydro, or whatever, we are talking about differential gears, and the tranny is irrelevant in this conversation.
(I do believe the biggest reason for using a Powerglide is to keep from wasting time shifting more than once, but torque manipulation may come into play here also.)
To get back to the original subject of this thread, I don't believe putting a smaller diameter tire on a car (such as a Super Charged XF) is going to cause it to actually have a slower velocity in the 1/4 mile as long as you haven't reached red line. And I don't believe an SRT with its 3:07 rear end, would ever be in danger of running out of RPM in the 1/4 mile by using only its non-overdrive gears. (As long as the tire isn't any smaller in diameter than what's currently used on the front)
It's been my experience in the few, turbocharged, and supercharged cars that I have ridden in, that it feels as though the car just keeps pulling stronger to red line than a normally aspirated car feels. Maybe that's why I don't feel an SRT would be susceptible to that "running out of steam" scenario that you are describing.