I know this has been discussed, probably at nauseum, but It's time for me to have my Diff rebuilt on my 2005 M3 ZCP with a 6 Speed and I'm considering Diffsonline with the Wavetrac LSD. Just curious of what Gear ratio people on here prefer and why. I was thinking of going 4.10 and some people seem to love that ratio, but there have also been some that considered it a not so good Ratio for whatever reason that is. I heard that for 6 speed cars, the 4.10 is the one to go with and 3.91 for SMG cars, but I was wondering if 3.91 would be the sweet spot, since my car's tune has removed the Speed limiter, so my Top speed will not be affected so much, but some gains in acceleration. So! before I spend $5000 plus on this thing, I want to know the Pro's and Con's of each ratio. My worry is that with the 4.10, my 1st gear would be useless. My Mods currently are full Supersprint exhaust, Eventuri Intake, DUDMD tune, HR Sway Bars and Wheel spacers and DMG front and rear strut. Any suggestions from the experts will be so much appreciated.