Clock Speed Question

Quick question on processor clock speeds and how it affects 4k editing. I work at multiple locations and we have workstations at each building, my home computer recently failed and I am running a back-up computer just to get by.

A computer tech that I work with all time has several HP 440's that's were pulled out of service and I can have one of those if I like. The HP440 is fine for at home because 90% of what I do at the house is Photoshop and Indesign. Sometimes I do need to edit some 4k footage on the weekend but very simple stuff and it's all from a Sony camera running their internal codec.

He has one 14 core machine but the clock speed is only 2.6. Is that trouble to get playback with 4k? I was under the impression that you need a fast clock for playback. I have a GTX 970 that I can throw in for the graphics card.

Thanks in advance.