I'm flying the autopilot in an RV-8 (about 10 hours now, so its a new install). Autopilot seems to working very well. The only real thing I've tuned is to bump up the turn rate limit to 3 deg/sec (standard rate turn).
yesterday I was making turns with ALT and HDG modes enabled, at about 180 knots. Spin the heading bug 90 degrees and the plane would roll up about 30 degrees or so, lose maybe 30 feet and smoothly turn to the new heading. GPS trk is a little better since the GPS track data is better behaved than the magnetometer (I haven't calibrated it yet).