You won't have any issue with any T-series Skylake or higher on a single 1080. A company I worked for ran a Kaby Lake i7-T processor on an 8x1070Ti rig for quite a while with minimal performance impact. unfortunately i don't have any true metrics to share, just anecdotes. i run an ancient xeon v2 right now in my rig and perf is adequate as well.
Remember that overall you will not be using most of the processor's power running hashcat on a single GPU, so you will likely see little difference if you did some Turbo Boost tuning and undervolted.
Remember that overall you will not be using most of the processor's power running hashcat on a single GPU, so you will likely see little difference if you did some Turbo Boost tuning and undervolted.