I'm going to suggest the Kingman Fasta 9v. It'll keep up with 12.5 just fine, and if you're good with a soldering iron and a dremel you can make it an 18v. It's $50, has nice capacity, and it's profile isn't really that big (Some people will say it's like playing with a whale, I never noticed an issue).
You may call it fat, I call it bounce padding.
If I say "the safety frame claim is bull****" I'm not ripping on PE, the SL8R is my favorite gun EVER. If I say "DMs are overpriced" it doesn't mean Dye is a bad company, I want an NT11 in the worst way.
However, when I say "The Vapor is overpriced and not very good" I mean it. I won't have one unless it's cheaper than what I can get a G5 or Proton for or free.