The 107 is only used by the KV, KV3, and SU-85 (which has the TD version of the 107).
The Su-100 has two TD 85s, the TD version of 100 D10T, and the TD version of the slow 122 gun (the t-43 has the 122 derp, which is completely different). I found that the 100 works best for the SU-100 since it has good pen, ok damage, ok accuracy, and ok RPM. The 122 packs a good punch, but it's slow to load, not very accurate, and expensive to run (1k cr per round).
I upgraded to the Slugger couple days ago, and already miss the 105 from the Wolverine. It wasn't a particularly fast or accurate derp gun, but it gave me a nice punch against all the high tier tanks. It's going to be a long grind getting the 90 for the Slugger..
My Hummel has had a run of bad luck lately where no matter how well I do, the rest of the team finds a way to lose the game. Team after team after team of people who lemming up into a big group, drive down one flank, and all get killed without don't any killing themselves. Or worse yet teams that just sit in the starting zone, and wait for their daily dose of shelling. At least the hummel is fully upgraded, so only a few hundred more games till I get the GW P!