The Crescendos are pretty solid amps. They can't quite keep up with the others mentioned though (unfortunately). I don't know what f'n boards they use or buildhouse or any of that conspiracy crap. All I know is the amps I've owned and tested... the BC3500 isn't as strong as the SAZ and not even the DC (which I wasn't really all that impressed with for how much they cost).
As far as the Sundown goes... his 3500 is basically a 4k so it's not a super fair fight. But even so... I would NEVER pay Sundown's MAP. No way.
In the grand scheme of things, they're all reliable amps. The difference between the top of tier 1 3-4k's and the bottom of tier 2 3-4k's is ~ 1,000w. Perhaps 1,500w wired to crackhead loads and on burps. The difference between them on the street would be waaaaay less. A few hundred watts probably.
The two nastiest 3k's I've ever owned or tested are the D5 and the B2 Zero.5. I've run them both daily and honestly.... if you sneaked a BC3500 in there without my knowledge, I wouldn't know the difference. The TL might though.
"On the street" is where Sundown and DD start to shine. They do really well on lower voltage and higher loads. Like... seeing 12.5v rising to 2.5 ohms or whatever. I love my cheater amps, but the fact of the matter is that you kind of HAVE to run the balls off of them to get the power. My D5 will still skull drag a BC3500, but then again... the 'nendo is a whole lot cheaper.