Probably because they are running stock 16*....if not lower than stock to get away with a smaller pulley...or pig rich to prevent the knock. I'd like to see those bin files.
There are also side effects of lower timing...higher EGT's being the main one, higher EGT's, higher temps in the motor from more boost on the smaller pulley = not a happy 3800
I'd honestly...like I said before...keep the 3.4"...and timing the crap out of it...see how much you can get away with. I'd bet it would run like a raped ape on 20-22*