I shoot an E-M10 with 2xZ240.
I have asked myself the same question many times. What would be a reasonable upgrade?
To ME, the only logical answer is to keep shooting what I have until I'm ready to buy a full-frame mirrorless.
The E-M1 II would be a really nice upgrade, just comparing camera to camera. But, I agree with @hyp. The differences, in the grand scheme of the pictures I take, is pretty small. And the cost of the camera itself plus the housing for it is just not worth it. If I'm going to spend that much, I'll spend the extra to go full-frame. Today, if I were buying, I would get the Sony a7r III. 42MP and the much larger sensor would, I think, make a REAL difference to some of my photos.
The crop factor and especially the way it affects ISO is a big deal with the m43 sensor - to me, anyway. I have to shoot at ISO 200 to have the equivalent of ISO 800 in a full-frame sensor. That is, of course, based on all other factors being equal and does not take into account comparing a newer, "better" m43 sensor to an older "less nice" FF sensor. The crop factor and its effect on ISO means that I can never get the same IQ as a comparable quality FF sensor shooting at ISO 100. I would need to be able to shoot at ISO 25...
Regardless of the technical details, the fact remains, upgrading to an E-M1 II is just not worth the $4K or so that it would cost me.
I am also not sure if it's worth upgrading from Inon Z240 to Z330s, either. I very, very rarely shoot with a full dump on the strobes. Mine are usually set at 1/2 power or less. In that case, would a Z330 really be useful? I think it would only be a useful upgrade for the very rare times that I am shooting on Full and still not getting enough light. But, I am all ears if there is a reason I don't know. I definitely do NOT count myself as an expert.
As an aside, I saw today on the Seafrogs website that they are now offering strobes that look like a total knock-off of the Z330. Same specs. Same basic housing design and controls. Not exact, but VERY similar. Rated for 100m/330' depth. And they are $297 each (less on AliExpress). The Seafrogs ST-100 Pro. I was actually thinking of ordering a pair to test and compare to my Z240s. The price makes them very tempting!
Edited by stuartv, 19 June 2018 - 11:15 AM.