What exactly would you like to know? I flew 600's on and off. The only complaint that I had were the Lycoming engines, temp. sensitive, underpowered and were known for their mechanical problems. Otherwise it was a great plane to fly, it beat flying around in the tiny Lears. The 601's had GE engines, I don't know anything about their performance.
I used to fly a 601-1b (601 with cf-34-3a engines and 45K mgtow) without a tail tank. Not a bad plane. Lot's-O-power up to about 16K' (remember the CF34 was developed for the A-10 and S-3, niether designed to operate much above the high teens). Quiet impressive runway performance (with carbon on carbon brakes). Like the fellow above said, nice roomy cockpit, no big problems. It has triple redundancy pretty much through out, but as many Gulfstream drivers will point out, it needs triple redundant systems because they are prone to small failures. The newer airplanes have a better reputation for reliability than the 600 and early 601s. I enjoyed flying it. It was not nearly as much of a "pilot's airplane" as the Learjets, but the room, APU and excellent HVAC made up for it. It took a little getting used to coming down the glide path with the nose below the horizon in a jet airplane.