Keep in mind it hits as hard as a Tier-10 IS4 (440-avg dmg per shot), with standard AP pen better than the "Tier-6 Dominator" - KV-1S with 122-mm gun.
Even the Gold Pen "less Pen value" - is still +1-mm more (176) than the KV-1S (175), and then starts hitting for greater than Tier-10 IS-7 dmg (510 per shot).
Accuracy and aim time both much better than KV-1S as well. Speed is not really a hinderance, though I'm sure acceleration is not "great", at 35-kmh - meaning it can keep pace with (albeit a bit behind) most of the big tanks that might be in a TC or standard Tier-6 fight in pubs.
Also keep in mind that RPM of 3.75 = 16 seconds per shot, by default. However, add in rammer (-1.6 seconds), and you are immediately down to 14.4 seconds per shot. With Vents, I suspect another 0.4-0.5 will be knocked off as well. With Brothers in Arms, completing the trifecta of RPM increasing skills/equips, you are likely down to about 13-seconds per shot. I think that is better than KV-1S gun. Granted, the lack of a turret is a hinderance, and it would remain to be seen how good the left/right gun movement is on this thing, but I can definitely seeing it being a powerful tank in Tier-6 battles, and would think you'd see a few in Tier-6 Medium TC's as well, for their defensive / or offensive (in support of KV-1S pushes) - capabilities.