I'm guessing the SMC Pentax 50-200 was introduced to match the traditional 35mm 75-300mm range taking into account the 1.5 digital crop factor? It would be a tempting lens, though it seems awfully light (255g or so?), keeping in mind that I may wish to use it hand-held too sometimes.

You mean the SMC 50-200mm f4.5 - 5.6 DA ED? The UK Pentax website doesn't appear to list any DA series long zoom lenses.

I'd have to see if I'd be willing to give up the extra reach. One of my holidays next year will be a safari, and judging by previous experiences I'd appreciate the extra length.