You won't use the 1st over, 2nd over. Go read reviews from actual owners, 90% of them say it's useless for anything but a highway OD, with gear splitting too insignificant to produce an ET gain at the track. IMO selling your 727 and doing a 518 would be more cost effective and more useful than the GV. If I was in your shoes I would definitely still consider it.
Also FWIW, I almost never need to downshift to pass with my 1.8L stick shift daily driver. I would have to question the driver if passing downshifts are something you need to worry about with a 400+ cube engine.
I like to keep a balanced view of products I'm researching, could you link me to some discussions? I keep finding positive reviews.
I'm too lazy to do a search for you, but there's been plenty of discussion about it on this website coming from actual GV owners. Overdrives are great, makes these old cars way more driveable. I wouldn't put too much faith in the gear splitting marketing goodness. Some food for thought, a 408 or 440 has a very broad torque curve. A 2.45 first gear x .8 = 1.96. Second gear is 1.45, close enough that a good aftermarket torque converter should hide most of that difference. A 1.45 second gear x .8 = 1.16. Third is 1.00.
