Tier 7- IS
Similar to the KV-85, the IS’s short-range mobility is second to none. Its traverse speeds are exceptional, the power-to-weight ratio is a very respectable 15 hp/t, accompanied by a 34 km/h top speed limit. It also shares a complete lack of armor for its respective Tier (save for the odd extreme angle), but what it does gain is a brutal 122mm with 390 alpha damage and 175mm of penetration on its standard ammunition – more than enough for Tier 7.
Sure, the KV-85 can mount a 122mm too, but after its transition from the old KV-1S to the current KV-85, the 122mm gun was absolutely butchered in regards to DPM and gun handling and isn’t even worth looking at, unlike the outstanding firepower on the IS.