Yes, I have mixed alky with gas at a 15% level back in the early/mid 90s, before moving to 100% alky.
The engine was a 462 BBC, oval port heads (049 castings), with a Crane Cam (.648/.669 solid flat tappet). 9.5:1 static compression with 8 Lbs of blower boost from a B&M Powercharger 250 (equiv of 4-71).
The carb was produced from a local supplier called C&M (no longer in business to my knowledge). The carb looked pretty much like the precursor to the Holley HP line. It started as a 750 CFM Double pumped, but wound up flowing 1020 CFM after they were done with it. I really regret having sold the carb, it was a nice piece.
We were running 93 octane pump gas through the motor with the 15% mix. The motor ran cooler, and we had zero issues with detonation. I don't recall how much it picked up, but I do recall a lower e.t. with the mix. It could have either been due to the decreased air charge?
Who knows. I know it worked, and thats all I cared about. We tried higher percentages of alky, but the fuel separated too much.