Banging off of the rev limiter at 7000 rpm numerous times and no problems yet---although I have an auto and I heard the manuals are a little rougher on the tensioner/belts if you powershift.
The frankentensioner----not pretty for sure, but it works. Also, (I know you know this 5twenty---but for others) make sure when you adjust the belt tension, that the tensioner is in the middle of the range of motion, giving the tensioner room to move both up and down.
2006 Mustang GT
572 cid BBF 924 hp / 781 tq
9.168 @ 149.65 mph @ 3420 lbs, all motor
8.715 @ 156.19 mph 200 shot