I'm one of the lucky people who bought the Sigma 50-150mm f/2.8 HSM just before they discontinued it, and I don't think I'll EVER get rid of that lens. Like FrogFish said, it's sharp even wide-open, and autofocus is fast and silent. I've had a "saved search" on eBay for the last several months to alert me when a 50-150mm is listed (so I can let people on here know), and in that time there's only been one or two that came up for sale.
All that being said, everybody who has the Pentax 50-135mm also sings its praises (except for those who have been burned by SDM failure!) Since the 50-150mm is no longer available, I'd probably go with the 50-135mm if I didn't feel like lugging around a 70-200mm and I didn't require the absolute fastest focus speed. But I would be sure to buy an extended warranty with the 50-135mm for peace of mind.
Have you considered the Sigma 85mm f/1.4 instead? Seems like it would be a good lens for a wedding photographer. It could kill two birds with one stone by giving you some reach, along with an extremely fast aperture for working in low light or for blurring backgrounds. And from what I've heard, the HSM is fast and accurate. Fast 85's seem to be popular with wedding photographers. Here's a review from a professional wedding photog about the Sigma 85mm:
Review: Sigma 85mm f/1.4 Ryan Brenizer — NYC Wedding Photographer. Problem solver, storyteller.