Given that CAT3 is spec'd only to 16MHz, * and CAT5 is spec'd to 100Mhz, you
might run into problems with wideband signals.

As this cabling isn't horribly expensive, why not use CAT5?

* I'm obliged to anticipate the obvious objection -- "But that doesn't mean it
won't work at 100MHz." True. But it isn't spec'd at that frequency, so you
have no guarantee how it will perform.