Well, I don't know if you could call it 'testing', but I did get on the beta server and try some stuff out. Here are the boring and not very detailed details --
I rolled my electric/stone tanker on the test server, played through the tutorial (Isolator!) and on up to level 5 when finally she was done in by vahzilok, at which point I stopped and took a break. Didn't really feel much different through those levels.
Earlier that same day I'd played a sr/claws tanker up to level 5 on one of the regular servers, so I duped that rare tanker on the test server and played up to level 6. The one on the test server had a much, I dunno, smoother time of it. Not sure if any of the accolade bonuses were a factor, but having the first two attacks switched did make a difference. I wound up not even taking the wimpier of the two, just going with that one attack. Later I went back to the one on the regular server and played up to level 8 or so. The test version definitely had it better, and was also much luckier -- got the Negotiator badge contact very quickly, and didn't get sent (twice!) to missions at the top of KR where level 13 clockwork lurk waiting for victims of contact maleficence.
Then logged back onto the electric/stone tanker and struggled on through that vahzilok mission, then leveled her on up to 27, same as her current level on the regular servers (27 being the highest level I've attained thus far on any of my tankers, the other 27 being dark/staff, which offers much wootness, btw). Loaded up with SOs and ran some missions, all solo. Still didn't notice much difference, aside from some of the accolade power bonuses.
Then I got all crazy and rolled a stone/ss tanker and went straight to 50 and goofed around for a while in PI. Having never played a stone tanker to that level, I have no basis for comparison. But I did play an /ss back in the day, so... well... I can't really remember much about it, except that at the time I thought it was, ya know, awesome. Seemed pretty awesome still. I was having fun and kinda forgot to double stack the rage thing to experience the crash. Woopsie.
Anyway, that's my 'test' results so far.