I've had the 4.10 in my car since I put about 5000 miles on the car..it is fantastic and at this point I have every major bolt on you can do. This and the monoball were the best mod investments I made until I ought the SC.
Good news is that my supercharger from VF just came in today!! I went the more modest route with the 540 as I live in MA and wanted to see the modulation and when I get tired of the 540 I can upgrade and find new love with the car.
Where I live there are not a lot of Ms. A few SC M cars, but not a lot. Went non intercooled because it is not excessively hot during the year. I do have a Audi TTRS that's stage 2 and I do see the difference in the larger intercooler during hotter days. So I am sure I will go that route sooner than Later.
You definitely shift a lot with this gear ratio.. One thing I will say as I regained more top end speed with the 20s.. Not a lot but definitely more than the 19s offered.
Bad news is that it is cold out now so with the M going in for surgery next week, I don't know how much of a review I will be able to do until march or so.
I do hope though that with the addition of the SC, all the STIs, charger/challenger SRTs and and the random GT-Rs I will be able to shake off my tail a little more. Felt so annoyed a few ago with a spirited run and a challenger SRT8 I could not possibly pull away from. And he was driving as possibly close to my bumper it was a little dangerous. I showed him that I may not gain space, I can certainly stop quicker than he can!!!
For any 6MT owner, this is a great investment. Very useful And fun on everyday driving and has made the track a lot more engaging as well.
I will report back once I get the SC and let you know my two cents if interested.