I think the trend started with Britcon!
Ok, personally I find normal gargants too fragile for my all ahead tactics

Otherwise I use a hell of a lot more flakwagons. I would also urge you to consider a 6 strong fighter bomber squadron. They pretty much always get through and if there is a guard/deathstrike player, this could be a good thing! Still you give up an activation...
Likewise with Orks trading activations for big formations is rarely a bad choice, unless that activation is a vehicle for the special weapon.
Of your options I'm finding the big blitz with supas nigh compulsory. You can double turn one and place bms over a cluster of enemy formations and mess up their activations.
My config for blitz brigades is always 2 flak out front to take casualties, 1 zap in the middle and one gun wagon at the back to take the bm when you try and sustain.
I would question adding the big guns to the boyz mob. You cut their move down to 10cm and boyz are bst when doubling. Big gunz are best starting the game on overwatch!
With that in mind if you were going to make a few small alterations I would go with (note I'm trying to resist simply saying you should take one of my favoured Ork lists

)
Note multiple threats are always good. So instead fo just one WE mob, 2 are probably better and if untouched can mutually support.
650 Gargant (BTS)
150 Fighta bommers
150 Fighta bommers
315 Warband + Battlefortress
315 Warband + Battlefortress
350 Big Blitz (2 x supa) Brigade
200 Blitz (zap) Brigade
200 Blitz (zap) Brigade
150 Stormboyz
150 Kommandos
200 Warband - I would swap for 7 skorcha and one buggy and get mobile FF support for your battlefortress charge!
175 Big guns + Zap
This last chap sits on an objective and garrissons on overwatch. Anyone trying to double - zap, blow away a transport while its loaded, and so on. I like to use two.
Sadly this makes you 5 points over, so you would have to make changes (drop a fighter, have a 5 strong squadron and get another flakwagon?) but its hopefully shows you a rapidly moving assault army.
The problem with it of course is the gargant can't keep up! But don't let that deter you

(You could swap it for 2 more mobs in battlefortresses!

)
How do you intend to use teh gargant? I like aggressive great gargants personally, can't abide hanging about on the blitz trying to sustain.
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