The only reason I went to 10.8gr with the 180gr XTP, was Mike McNett had posted that load in his STOCK G29 in the IMR data thread. It hit 1263fps. That's pretty impressive out of a stock G29. I didn't see any bad pressure signs, absolutely no Glocksmiles, and max case expansion was .4335" (.435" being my max).
Actually the ONLY load I've ever stopped myself on was 12.0gr of 800-X with a 155gr XTP. I had some 12.2gr loads mixed up, but didn't shoot them. Slide velocity was so extreme on the 12.0gr loads that the slide was coming back so fast it would catch and crush the brass before it could ever leave the gun. I also saw one TINY Glocksmile with that load. That was actually the only Glocksmile I've ever produced with handloads.
I'm fairly certain you could go to 9.5gr or higher with the 200gr XTP (not that you really need to). McNett posted 38,500psi for 10.0gr 800-X under the 200gr XTP, and I believe all of his loads were with MAGNUM primers. I would guess pressure would be a little lower with standard primers.