I recently purchased a modded '98 M3 Sedan. The car is pretty quick as it has quite a bit of power-adding upgrades. I was wondering if there is a bolt-on 6 speed transmission for my car. The revs are quite high at highway speeds with the 5-speed and it is has plenty of torque for low RPM passing, only thing is, it gets up there so fast and run out of gear. Speeds approach mid triple digits quickly. Reasons for extra cog: 1) Lower cruising RPM 2) Higher top speed Concerns in switching: 1) Durability 2) Fitment 3) Cost-prohibitive 4) Potentially shorter lower gears (ex: When I turbocharged my '00 Miata, I had the factory 5-speed. I was planning on upgrading to the factory 6-speed only to find out that the first 5 gears in the 6-speed were equivalent to the first 4 in the 5-speed, rendering the swap useless has I gone through with it) Any input or guidance on this would be greatly appreciated.