Considering buying the HS30

Yes, 810 EFL, but when further cropping to 8mm image circle (the HS30's sensor size).

Think of it this way: full-format's image circle diameter is 43.2mm, M43's is 21.6mm, HS30's is 8mm.

The FOV (field of view) of lens with physical 150mm FL becomes 300mm equivalent when cropping to 21.6mm, but 810mm equivalent when cropping to 8mm.

Of course, you'll get only 2.2MPix when you crop G3's sensor area to 6.4x4.8mm (8mm diagonal) size - as opposed to HS30's 16MPix.

But frankly: it's illusionary to expect high quality pixels from small sensor camera: those pixel are just very small. You'll end up downsampling the HS30's 16Mpix output to a more reasonable pixelcount; maybe to target pixel count higher than 2.2MPix but not much.