I'm building a deck with 5/4x6 Trex and pressure-treated framing.

I was shocked to see that steps require not only 12" spacing on the
stringers, but also the use of 2x treads (instead of 5/4 thickness).

Can someone who's built steps with Trex confirm or deny that it's
really necessary to build steps this heavily ? I do plan to have
vertical boards between the treads (whatever they're called) but I
guess I can't use these to help support the nose part of the tread
without violating the gapping rules.

I don't mind spending a little extra for the 2x6 if necessary, but it's
a pain, because I'm using the simulated-woodgrain "Accent" boards on
the deck itself, and the lumberyard is making a big deal about getting
2x6s in Accent (as opposed to the plain finish); they can't even quote
a price and it's a special order and all that. Or maybe it
wouldn't be so bad to just have the plain finish on the treads.

Please advise !

Thanks, John