First of all, if you go down the GR Bass road, only the 800 Watts or more heads (and combos) have the option of the off (silent) fan, which is a great plus in studio or mire silent places.
The more power under the hood, the more headroom and definition you have, especially in the low end.
I would use their AT 212+, which is 900 Watts (full carbon iteration and the most powerful) in 8 Ohms and you could use two for the heaviest gigs and/or bands.
It's all very light, powerful, reliable and excellent sounding.
I've used various versions if their gear over the time and it's always been a delight.