Check out the recent thread :
TCS 9x11 3800 First impressions
http://turbobuick.com/forums/showthread.php?s=&threadid=136263
It has a discussion about the 3800 9x11. Basically what it says is that while the 3800 stall helps with the lower end and launching, the top end suffers because it is too loose and puts the car out of the upper end of the power band.
I am not quite sure, but in the thread it seems even with the torque converter locked up there isn't sufficient RPM drop to keep it in the power band. Although theoretically, the lockup should make a direct coupling and load the motor sufficiently to do so.
Could the internals used in a 3800 stall 9x11 differ from a 3600 (and below) 9x11 ??? I ask this because I don't think I have seen or heard of this being an issue with the 3600 and below 9x11s. I personally have a 3600 9x11 with a GT67 turbo, while I haven't gotten to a track with this combo yet, Turbolink is showing significant RPM drop when the converter is locked through the gears.
As an aside, there is a GN here locally with a PT61 and unopened engine. He switched to a 3800 9x11 (from a 3400) and his 60's improved (1.5-1.6), but he lost significant MPH (115), even when locked up. Putting back the 3400 netted him slightly worse 60's but better MPH again, netting him a best 11.1 @ 122 with 1.6 60's.....
If the 3800 9x11 behaved like the lower stall versions at the top end, while still having the wicked lower end, it would be a great converter.......IMHO.......