I have a 6505+ that I capture through a Countryman Type 10 DI and run through impulses, so I can compare the X50 and the 808 TSE to the real deal, power section, reactive load, impulse and all. The x50 is very impressive. It is missing a little bit of life in the high end and mids and it's less three dimensional, but it can provide sounds that are better than what is tracked on a lot of albums with the right impulse. The inaccuracies are just a sound like it's kind of smoothed over rather than nastier like the real thing.
I can't stress enough how superior it is to all other current plugins. It is the only one that comes close to the axefx's level of modeling.
Here is the X50 with an 18v EMG 81. The bass is running through it as well, but has a bass oriented chain running the lows under it. The riffage is bullshit made up for the test sorry.
Hopefully that kinda shows what it's all about to the ear holes.