Hey Kirk,
Actually I'm inclined to give them (Pearse) a try since the heaviest I've gone on strings ever was a .12 set. I think there was a set on the site that had slightly heavier bottom strings...I'd have to look again.
Re: flatwounds - Yeah I haven't used them in years because they do tend get dark and dull, but was curious of how hey worked with
slide. Sounds like it may not really make much of a difference.
GHS makes some "rollerwound" sets where the roundwounds are ground to a close to flat surface. I believe the "Nickel Rockers" and the Chrome Brites are that type. I think the D'Addario's you are talking about are called the Half Rounds or something to that effect. I haven't seen them in the stores for a long time but Juststrings.com probably has them.
I'll let you know if I get some in the near future.