The 200 isnt a weak trans when built right.
They were intended as light duty trannys for average joe cars, and had soft shifts, lighter (and cheaper) internal parts.
The BRF code trans out of GNs were built better, but were still not bullet-proof.
Take one to someone who doesnt know squat, and it will fail. (i made that mistake a few times before I learned my lesson). I had a dealer build mine twice. Came apart after a month or 2 of just daily driving. I went and had a pro build it, and it has been a couple of years now, and no problems at all.
You would certainly miss the overdrive and the locking t/c on a street car by going to a 400.