If you haven't made a choice yet, my $.02 is this:
The PMR SE is a great choice. It's got the metal back cap that you're going to have to replace anyway, and a much nicer trigger. Still not a trigger I like, but much nicer than stock PMR. Throw a Critical Raze on it, get it adjusted right, and there'd be no use for a UL frame, plenty fast and comfy stock (I personally prefer the stock frame to the PMR UL).
Another gun I'd seriously look into is the Invert Mini. Now that they're down to $325 new, you can get them $225 used. Throw the NDZ bolt and spring in there, and you can drop your pressure down to 130-140 psi, dwell down to 15 (from 28), and it's almost impossible to feel it kick. And very small and light of course.
In the <$400 range, these are the 2 guns I consider to be the best values.