Why not just remove the spring all together? I bought one of the lightweight replacements from the GB, but ended up liking no spring at all.

Synchro Rev is insufficient for racing. Our data showed that it doesn't blip the throttle on downshifts nearly high enough. It's good for the street and the casual track-day guy, but once you get serious about it, it's best to turn it off and manage the revs yourself.

OP, turn SRM back on and pay attention to the relationship between gear, speed, and RPMs. Learn how the car wants to you to drive it. You should be able to smoothly shift fast (harder on the clutch) or slow (easy on the clutch). The Z doesn't like the in between stuff.

As for turning SRM off, many people enjoy rev matching themselves. I keep it on most of the time to keep down the wear on my clutch. But I will often turn it off when I do some "spirited" driving through the hill country.

I never turn mine off, nothing like switching to lower gears when entering a turn and blasting out of it on the apex. LOVE synchrev for that. I am not the best stick driver, but that button makes my life nice and easy

OP with the stock clutch spring in I had the same issue, had to slip the clutch for what seemed like too long. That said I never actually burned the clutch doing this..*shrug*

Pull out the clutch spring entirely, you'll be much happier :)