Hi!
I really, really like all the changes, except for Baneblade.
I think 4+ for FF is correct, since a DC3 BB is mostly equal to 3 Leman Russ. The latter has 6 heavy bolter in total, the former has 3 but twin linked one.
All weaponry looks fine by the fluff [eleven barrels of hell!] and by the stats aswell.
The one and only issue in my humble opinion is the main battle cannon. It just doesn't have the punch and most of the time it's AP/AT just bounces off, like if it weren't a Super-Heavy Tank knocking on your doors!
Rug felt it right that the mb cannon must be buffed somehow. Range wouldn't solve anything, since it is the damage what is too soft, and if you would need a BB variant unit, hitting enemy from 90 cm range, why on earth would you take one with AP/AT 3+, instead of MW2+ TK(D3) ?
A close to middle (30 - 60 cm?) cannon volley, with raw firepower would more befit the fluff and the rank, that should differ from shadowsword.
I suggest the following stats for the main battle cannon:
WEAPON: Experimental Cannon v75
RANGE: 75 cm
FIREPOWER: MW4+
Or
WEAPON: Experimental Cannon v60
RANGE: 60 cm
FIREPOWER: MW3+
Or
WEAPON: Experimental Cannon v01
RANGE: 75 cm
FIREPOWER: MW3+
Macro attack is in short supply in the whole Steel Legion anyway.
Whereas v75 maintains the ability to attack deployment zone first round, it may still lack the sufficient punch with a 4+ hitting value as standard.
v60 is more significant change, since it denies the ability to attack deployment zone first round, but at the same time, maintains the 3+ hitting value and probability, which the original mb cannon had.
v01 is the combination of v75 and v60 with their best values. Meaning: Everything remains the same, just simply swapping the AP/AT into an MW dmg.
Erm, this was my two cents.
PS.: Even if v01 would be applied I still be tempted to take Stormblade variant, instead of Baneblade variant.
I know it is a question using Minervan or other lists that allows Stormblade.
Hmm, have you considered that these general changes, affects all other lists that use the same stuff ? (upgrades, BB, Emperor Battleship)