Here's my personal experience with the 18" Gunner barrel.
This is just my opinion from my real-world experience.
1. Stay away from ultra slim handguards that cover the gas block.
My original handguard was an ultra slim handguard, and the increased barrel whip had the upper portion of the gas block banging against the interior of the upper rail. This was even with the very small Faxon brand .625 gas block. This threw off the shot and I was just chasing a zero.
2. Stick with Faxon's .625 gas block. It's truly the narrowest of any .625 gas block I found, and having 3 set screws is nice.
I'd recommend Aero's Enhanced, Quantum, or R-One handguards if you want to cover the gas block. If not, then one can choose what I did and leave the gas block exposed, sort of like a MK12 look.