Ah GM, a love of mine that I've sadly let go
I've had a few GMs (about 11 off the top of my head) so feel fairly qualified to comment on this!
The octane has a very low middle and picks up heavy. It has a lot of wood in the hitting area for a front foot player, but back foot shots that came higher off the blade could feel a bit 'vibratey'.
The Icon is well, an icon! Mine had a very nice pickup (nobody ever guessed it was 2lb13 from waving it round!) and had a lovely long sweet spot. Don't let the "high middle" put you off, it's a good bat for shots all round.
Another bat I'd suggest is the Six6.
F4.5 face so not massively rounded and not dead flat. The balance and pickup is good and the sweetspot on the ones I owned was lovely and long. If you can get one to play with before you buy id recommend it.
The Mogul I haven't personally used but I love the shape. Maybe a mid-season purchase if I have an emergency!