ugh, don't SBR that gun, please!
You're giving up so much when you SBR a .308
it's literally PERFECT the way it is.
PLEASE PLEASE PLEASE don't ruin something this wonderful by chopping it up!
Unless the OP is going for long-range accuracy, I agree...it's too much barrel on the front of that thing, especially with the suppressor. For a 100-200 yard range, an SBR ought to be fine. And you conserve a little energy with the suppressor as well.
You have each firearm for different reasons and IMHO a 20 inch barrel at range will be much more accurate than at 13'. So if you really want to reach out and touch someone leave it long. It you want to know something off its feet at 200 yards chopit. What do you think?