Videomaker – Learn video production and editing, camera reviews › Forums › Cameras and Camcorders › Professional Camcorders › What camera would you suggest? › That was what I was warning
That was what I was warning about the X70 as well as the Z90. You lose some control since you don't have those extra rings (the one ring on the X70/Z90/NX80 is for either Zoom or focus). I would say if you want the experience of having control of those then get the NX5R like Paulears was saying or the Panasonic UX90. I do think it is worth it to have the extra rings just for the control they provide. As for 4k, I would recommend everyone start upgrading that way, but since you seem to be doing this on a non-professional basis (from your original post), if your computer doesn't have the capacity for 4k I'd say don't worry about it. 4K file sizes depend on what codec you use, the Z90 uses a 100mbps codec so the file sizes are very manageable compared to a Canon XC15 where the codec is 305mbps and those files are huge.
Is it worth it to have 4k over extra control? From what info you've provided us I would say you could do with both. I think you would love the images that 4k provides with the control of the rings (Panasonic AG-UX90). If you think 4K is too much, which is okay because 4K is a beast in itself, then I would say get the Sony NX5R or NX100.
It really is up to you. All we can do is give you our opinion on specs and real world experience.