I had to deal with this myself fairly recently. I had intended to use 6a everywhere until I encountered the power/heat that it took to run each link at 10Gb. Damn, that stuff gets hot! I came to the realization that 2.5Gb was probably going to be the practical limit. Handling the heat for running 10Gb copper makes the case for optics even more compelling.

Our Cat-6a plan went out the window in favor of OM3.

Protip: I "knew" that optics were hard, expensive, and were a nightmare to work with. I was very, very wrong. OM3/multimode is relatively cheap and far more tolerant than I expected. SFP+ DAC cables also have compelling use cases.