I'm pushing around 1400hp thru a stock T56 Magnum in my 88mm turbo 6.2liter RX-7 and no issues. I don't powershift it... and haven't launched hard.
Had over 700 very very hard miles on it. All over 1000rwhp setting.
It ran 9.35@163mph with more left in it. Launching with zero boost and normal shifting.... not foot to the floor. The shifting quality of the Magnum is light years ahead of any 2006 and older style T56.
https://www.youtube.com/watch?v=y472n4EbWO0
Some people can break anything.... if you simply drive it too hard. But for $3K the T56 Magnum takes a serious beating. Even in 5th gear it takes 1400hp which is much weaker than the other gears.
I have one in my LS7 RX-7 also and it kicks *ss.
__________________
Project: 1969 Chevelle, alum 5.3, GTS76 turbo, Chiseled Perf A/W intercooler, Holley Dominator EFI, Davis TC, JRi coilovers, 14" brakes, T56 Magnum. CTS-V Recaro seats!
Coffey Fabrication Nashville, TN doing the fabwork! 800rwhp+/25mpg+/9's@150mph goal
https://lateral-g.net/forums/showthread.php4?t=52976
1993 Mazda FD RX-7, built LS7, T56 Magnum, Holley HP, Davis Tech TC, 8.8" 3.73 Cobra IRS diff, DSS axles, Ohlins coilovers, big brakes.
CCW 18x11 front 315/30/18's and 18x12.5 rear on 335/30/18 RA1's,
2850lbs
10.31@137mph 165mph Shift-Sector 1/2 mile speed
441ci AllPro headed motor and 200lb weigh reduction in the works....