Gaming perf is affected. Lots of vids on the youtubes proving this. Impact ranges from zero to twenty percent, depending on the CPU in use, the game, operating system, etc. Most games are either totally unaffected or affected within margin of error 1-2% which could just be margin of error rather than actual perf degradation.
For most gamers on most intel CPUs the in MOST games the difference is not going to be noticed. 4770K is still a decent CPU. You can overclock them quite a bit, and you should. It helps.
Broadwell is just a die shrink of Haswell and as such doesn't offer much of a performance bump. Also Desktop broadwell CPUs were on the market for like a month (if that) before being replaced by skylake and as such they are kind of odd-ball collectors items now and fetch outrageous prices. Not many floating around, as nobody bought them since people knew Skylake was around the corner. Honestly I have no idea what Intel were thinking releasing the 5XXX series CPUs for like 30 days and then replacing with 6XXX... makes no sense to me... why bother manufacturing them? For what a broadwell i7 would cost you, you could probably pick up a 6 core ryzen, mobo, and some DDR4.
(Mildly interesting pointless drivel
AFAIK they put out broadwell and used it in OEM machines for a few months because they were having issues getting Skylake yields up with 14nm being pretty new at the time and it was probably easier to mfg a die shrunk haswell on 14nm than a brand new architecture.
