haha, I'm going through the same machinations myself right now, so I get it.
I know you don't like the quad rails (I've come back to a gun with a DD M4 on it recently and with the Larue index clips really like it) but you might think about a standard 12.5" barrel with an FSP cutout handguard. That way you're not adding the extra weight of the gas block (which is only ~1 oz. FYI) but you're still getting a fixed FSP.
I've been thinking about ordering a Centurion 12.5" barreled upper with his 12.0 FSP rail on it. Since I care less and less every day about a can, I can't think of any real downsides to this.
I'd like to see more Brazilian-style handguards with FSP options. I swear I had seen an Apex like that.. maybe it was a custom cutout on one of these.
http://www.apexhandguard.com/store.p...=112348#images