Another nonsense-comment for FF vs APS-C options:
Switch to FF could be interesting not only because of "better IQ". You also make a switch to opportunity 'to use a lot of lenses that were made for FF cameras in last few dozens of years'.
And that's a lot of fun!
For example, last week I decided that probably it is the time to investigate universe through 'fish-eye' (without spending too much) and got some cheapy-trashy-manual $200 Zenitar 16/2.8 lens.
Today I finally had an opportunity to test it for my normal 'way of work', that's shooting pictures of print equipment for our magazine's tests & reviews.
Yes, the result is too soft, with bad CA and just horrible (f/8 with ISO 1600 in not very bright office room + quick PP in Aperture). But: no crop camera can do the same with $200 lens.
Few more days of experiments and fun with this lens will probably help...
Interesting shots, I didn't realize fisheye lenses longer than 15mm existed. 16mm isn't much longer, but still it's interesting