I was thinking exactly the same thing as far as keeping the M8 for IR work. I plan to get an M9 or ME in the near future (a year or 2) and the M8 can be my poor man's MM, but for IR.
I have the B+W 092 for my Zeiss 50mm Planar and was going to start with that and see how it goes, but I think I'll pick up the 52mm and experiment with the 15 as well.
I lived in Seattle for 12 years so am familiar with some of those locations.
Which IR photos did you sell?