I'm also tempted by the 150 f2 - but it's an expensive piece of kit! I'm busy selling an elmarit APO 180 f2.8 - because I really don't use it that much, and it's too valuable to justify it's existence as an occasional lens . . . . actually, you're giving me dangerous ideas . . . ..
I've wanted the 150/2 since I first got into FourThirds. My reluctance is not just the price tag, it's the amount I'd actually use such a long lens. The 50-200 is superb, and I don't use it terribly much either, although last Saturday's session pointed out to me that the long-end focal lengths have their unique charm.
Olympus E-M1 + ZD 50-200mm + EC-14
ISO 200 @ f/5.6 @ 1/2500 @ 258mm
A 150mm f/2 would net me 1.5-2 stops faster for more DoF control, and a 210mm f/2.8 with the EC-14 is a luscious idea. But beyond that, the 150/2 has such absolutely beautiful image rendering ... sigh.
The 75 f1.8 is unmissable though - just buy it Godfrey - you know it makes sense!
Oh I know that. It does, it's likely the next lens I acquire, depending on when the Panasonic-Leica Summilux-DG 15mm f/1.8 ASPH is released. 75mm I do use, only thing keeping me from plunking down the cash is that i have three other lenses in the focal length range (Summicron-R 90mm, Nikkor-H 85mm, M-Rokkor 90mm) all of which do a beautiful job.
So many nice lenses to enjoy with these cameras!