Re: Shift kit and deraileur gears
I have been running mine for well over a year and haven't had any damage. The only time mine ever was damaged was when I let someone I didn't know ride the bike. Don't know what they did but it came back missing some teeth.
I think your assessment on the extended chain may be accurate. I would suggest removing a few links from your chain in an attempt to increase the tension on the chain. I have mine set so that when I am in the largest gear (1st), my derailleur arm is pointing forward at about a 45 degree angle. The way I see it you aren't in 1st very much and as you hit the taller gears it will straighten out to a more normal stance but will still have added tension over what you would have had without the shortened chain.