Telephoto(Wildlife) lens options?

It's now a few months since I sold my Canon stuff and went m4/3s(G3). I've loved having a system I can carry while backpacking up in the mountains. The other day I got some nice shots with the 100-300 of seals, sea ducks, and razorbills. But compared to the kind of wildlife shots I got with my 300 L f/4 IS, there is a sharpness and color vibrance missing except on the sunniest days. Also, no tripod collar. I see otters, owls, caribou, etc. that I want to shoot from the car or with a tripod. So I have been thinking about getting a bigger lens, mostly for tripod use, to use with my m4/3 camera, mostly for shooting wildlife. What are my options?

Ideally, Panasonic would come out with a 200, 250, or 300 f4 or f5.6--comparable to the Canon 300L f4 IS or 400L 5.6, but I ain't holding my breath. 2.8 aperture lenses are too heavy, so they're out. I'd spend around $1,000 for no IS ability. Does the aperture work when using a non m4/3s lens with a converter? Thanks for suggestions.