As long as you operate below 100K, TEB has no problem with the higher certification weight. I confirmed that with both Gulfstream and TEB. However, the ER will have a reversible placard to allow both max operating weights. It's still unclear to me whether a mechanic will have to make a logbook entry to change between weights or not. Similarly, ASC-026 restricts the G650 to 74,900 lbs should an operator need that flexibility.
I'll be as kind as I possibly can and say the G650's reliability has been poor. We've canceled far more trips in the past 6 months than I had previously in 15 years flying business jets. My boss has been stranded and had to charter on at least 6 occasions because we were AOG. Several other trips have been delayed, and the plane has constantly lived in service centers. I'm pretty sure we've never flown a leg that didn't result in multiple squawks. In contrast, during the entire 4 1/2 years in the Global, we missed one trip because of a mechanical problem. That said, Gulfstream is now making a serious effort to help us get this thing settled down. The support is very impressive, and I have no doubt someday this will be a great plane. Sadly, that day is not today.
In my opinion, the Global's interior is far superior in almost every way. It's roomier, it doesn't waste space with huge, loud and hot avionics cabinets, and the fit and finish and overall quality is much better. To be fair, I'd probably like it quite a bit better if things would stop failing every flight. In the cockpit, I hate all of the old school unnecessary button pushing and ridiculously long checklists. You might disagree, since I understand much of it pays homage to Gulfstream's going all the way back to the III. The Global's cockpit is much simpler and it is very quiet. We always took our headsets off in cruise in the Global; we pretty much have to keep the headsets on the entire flight in the 650. You may have heard there is an insane amount of airflow in the 650 cockpits that makes long legs pretty uncomfortable. I know one operator flies with one pack turned off to reduce the hurricane force winds in the cockpit.
There are plenty of good things about the G650 too. The trailing link gear and huge wings make for very soft landings. The performance is simply stunning in just about every way. We climb like a rocket ship at 320 transitioning to M.90. It goes fast and far, and it does it comfortably and efficiently. The cockpit seats are more comfortable on long legs than the old Global seats, (I've heard the new Global seats are good too) and the Planeview II is a huge step up from the old Primus 2000. (I imagine the Vision cockpit is good too) It's a cool plane with a great presence. I sincerely hope the boss doesn't give up on it before we have a chance to work out the kinks.
I went to recurrent last month, and I was a little surprised to hear we are not at all unique though we are definitely having more problems than most.