Well, I guess I'm "lucky" in a way...
After several back and forth shipping events of my 18 spline A833 that came in my 70 V-code Roadrunner, I replaced it with a 855 that has performed flawlessly.
It makes a little gear noise in the lowest gears (1st & 2nd) but that doesn't bother me, at all, and I guess it's reminiscent of the M-22 "rock crusher" although I've never heard one as far as I know. It's been great, under ALL circumstances, including power "no lift" shifting at the occasional track night. To be clear, I keep the gas pedal planted to keep the 6bbl open, but bump the clutch pedal to grab the next gear. I have put down the deposit on the "new" Bill Mitchell aluminum RB block, and I'm planning on a 6XX HP and close to 700 ft lb 540 cu in stroker build up.
If I ever have a problem with broken parts in the 855, my decision would be based on what caused the breakage. If it's too much power, then I'll have to look at another kind of 5 speed, have the 855 repaired, and sell it.
I am keeping my 18 spline 833 as a "spare" if I ever get it back from Passon, who has it for the 4th time now. Originally I sent it in because it was sloppy, but most of that was resolved by a correct Hurst Competition Plus shifter assembly and the correct hardware, vs the hot mess that was on it when I bought the car. I asked Passon to go through the 833 and replace anything that should be replaced, and while he was at it, install the "slick shift" synchros he advertises because I figured that would aid shift speed at the track. The 833 has performed better than I could ask, except that ever since Passon got it the 1st time, it pops out of 3rd gear. Now since I've had my 855, which I'll reiterate, works great under all circumstances, I've been without my 833 which Passon has had for over 2 years, to "finally" fix the 3rd gear popping out issue. If I get the 833 by the end of the year, I'll be happy, IF it doesn't pop out of gear in 3rd, and the only way I'm going to know that is the next time I have to drop the 855, for a clutch disc change or similar thing, unless I want to swap to test and then put the 855 back in once I'm satisfied that the 3rd gear issue is resolved. Although i have the 3.54 gears I removed and replaced with 4.10s once I installed the 855, and driving on 4.10s with the 833 would mean no 70 mph highway trips, I'd rather have the 833 for a spare and be able to drive some than have nothing should the 855 require a long repair time.
So I'm lucky that the 855 works great, but not so lucky that I'm without my 833, and that I've had to install and remove it 3 times now.