Since you have the UBC Comps in mind - and I'm delighted to hear that you do! - and also IPAS: I'd go with the Smith 586 or 686.
Nice hefty pistol, fully adjustable sights, and its bigger 10-round magazine is a lot better suited to reloading-on-the-run than are the 8-round magazines of "automatic"-styled Umarex pistols.
Jim