Considering a mix of single, lowly and heavily threaded programs a much faster quad core could still be better than a slower octa core for a while.
15-25% faster at 1,2,3,4 core loads then reverse from there? It won't be future proof maybe, but for today it's ok. If parallelization finds its course then heavy AVX2 usage will help it further.
Honestly it's all a moot point when in a few months hex core becomes mainstream for Intel too, we'll have a preview from skylake-x 6 cores reviews then coffelake will just be that +IGP and better clocks, hopefully.