In my opinion, there is absolutely 0 reasons to go with Quadro instead any of the Titans. Viewport won't be enhanced in any way and their only Quadro selling point is imaginary "stability" and "professional support". There is nothing that Quadro will do better apart from ripping your wallet apart.
Some time ago the selling point for Quadro was its >8bit color support, but that's not the case anymore since GTX 200 series I believe.
Mostly true.
For viewport in 3dsMax and 90perc. of CAD programs (the exception being Siemens NXT and some other obscure CADs, but not AutoCad for example), Quadro
don't provide better performance under Nitrous/DX11.
The current Quadro benefits still stand elsewhere:
14bit color pipeline support (no, GTX do not support it because...nVidia, just because).
ECC memory- ECC does not add any stability by default, it enables error correction in very rare cycles that would only be important in serious
scientific calculation. Rendering does not fall into this category.
Double floating point precision- same purpose as above, higher precision calculations. GPU rendering doesn't fall here either. This is crippled feature, as GTX/Titan could do it identically but it's "locked" away by nVIdia.
"Support" / "Special" Driver - Mostly marketing gimmicks, but could potentially be benefitial to software developer, but not end-user.