No problem. Make sure you visit the Gigabyte website and look at the support list for compatible CPUs.
Yea older hardware can be difficult to get. Much easier if you are OK getting it second hand though. TBH I really doubt you'll notice much of a performance difference between the Haswell Refresh (or Haswell) and Ivy Bridge. I do appreciate your concerns going for older tech in a new build though.
If you happy to give up the Thunderbolt, I would stick with the Z87 boards in the buyers guide. As long as the BIOS is updated, it will work with the 4790K. The Z97 are getting there, but it seems like unnecessary effort unless you plan on using the updated connections (M.2 and SATA express) or want to update to the Broadwell CPUs.
Again...appreciate they are getting harder to source now, but that would be my advice. My setup with the Z87 and 4770k was really easy!
Best of luck mate.