RE: gearing
I think it depends on the type of riding you intend to use it for.
The first thing I would do (and did) is get a Rekluse, then you will be less tempted to mess with the gearing. I ran the stock 13/52 gearing for 20 hours with the Rekluse and it felt good - the more I rode it the more it was okay. At first I was thinking about going much lower because I sucked at technical trails and I wanted to go slower. But then I also got a steering damper and a LHRB and those each helped somewhat, especially the damper - I didn't feel the bike was so busy going over obstacles and I wasn't working so hard. Bear in mind I suck at riding off-road, so this is compensation for my suckage until I get more experience/skill and build up my endurance.
Overall the Rekluse helped the most and is definitely worth it.
So I just put on a 12 tooth sprocket and left the rear alone. I tried it for one ride. On the pavement I noticed a significant difference at moderate to higher speeds. Sixth gear no longer lugged at 60 MPH but the bike could still easily hit 80 MPH so I could still get out of the way of cars if I have to on my way to/from the trails.
On the trails, because I mostly ride slow speeds in first and sometimes second, I noticed much less difference - which makes sense because any gearing change will have less impact at slow speeds - it is a percentage change and 10% of 5 to 10 MPH is just 0.5 to 1 MPH, whereas I lost a good 10 MPH at the top end. I may still leave it on or I may go back to a 13 tooth front after riding some more, but it is unlikely I will go any lower. I am also going to go with a trials tire, so the diameter of that may make a difference too.
As for problems. I haven't heard of any endemic/systemic problems. I don't have a lot of hours on mine yet, but so far it has been a great bike.
