I use my 150 on the Hasselblad quite a lot, both for landscapes and other kinds of things. If your vision works in a "less is more" sort of way, it's a good way to go. If you want to be very selective in your compositions, a 250 might be a better choice as an addition to your 150, rather than the 180. Aside from a converter, another good way to find out might be to rent one or both.