Well, the other proc won't change the mounting variation though. It's too bad I didn't keep one of the scissor brackets

I never thought TR would send me a heatsink w/ the old solid bracket. A few quick points though:
1. I tried using washer w/ the old scissor brackets to increase mounting pressure and that didn't change temps. Admittadly, I only used one flat washer (approx 1mm thick?), so that may have been a minor change.
2. The Maxorb mounting pressure is actually not created by the frame. The whole point of that frame is to just stick to the mainboard and not move. Tension is applied by a spring-like lever that latches onto the frame. As long as the frame doesn't move and is held at the proper height then it doesn't matter whether it is bolted on, clipped on, etc... I wish I could explain it better w/o you actually owning a Maxorb. Maybe if I get some pics of the Maxorb's tension clip?
3. The reason the heatsink doesn't rotate in the solid bracket has nothing to do w/ the mounting pressure. The heatsink can't be rotated because the bracket wraps over the sides of the heatsink and prevents rotation. However, that does not mean the solid bracket isn't resulting in increased mounting pressure for other reasons. It could very well be, and that could contribute to the 4C better performance (though I think the issue is perhaps w/ the base - the 3rd heatsink had a WAY better base than the 2nd).
4. If the difference between the 3rd heatsink and the 1st / 2nd is because of the bracket, then it just means that the 3rd is also no better than the Maxorb had it been mounted w/ the scissor clip. That, imho, is just as bad for TR as the 3rd heatsink being better. Either we have fairly large variation in TR's manufacturing resulting in fairly large variations in performance, or we have TR producing many defective heatsinks lately that are barely better than Maxorbs.
5. The CPU also can't explain the Maxorb comparison w/ the first two heatsinks. The only thing that can explain that would be if the Maxorb's slightly modified mounting did result in greater mounting pressure for it, but I explained that as best as possible in point 2

I'll need pics to explain it better.
So... The only thing I can think of out of all that which might explain it other than the TR quality itself... Maybe if the frame for the Maxorb was held marginally closer to the board using the screws than it would have been w/ the plastic push-pins (the push pins have a little spacer that raises them a certain height from the board). The difference though is certainly no more than the same height as the washers I used w/ the TR's to try to increase mounting pressure, and that made no difference. And.... even if that were the case, it doesn't explain other people who have posted complaining about their issues w/ TR (there've been a few other posters in this thread who've said their latest purchases from TR haven't been too great).
The only reason for me to try the other proc is to get certain people (not you) to be quiet, but in the end I know those people will latch onto something else, so I'm not too worried about it. I'd end up having to test iteration after iteration of stuff and eventually they wouldn't come to the same conclusions no matter the results, they'd just stop posting and let it drop, unable to determine what I'm doing wrong.