Have you been running synthetic for a while or will you be switching from dino?
0w? In TX?
My car has 10w-30 conventional in it, FWIW. From what I understand, for warmer climates, you want a heavier oil so that when the engine gets to operating temp your oil is still thick enough to lubricate everything. Also, for higher mileage/older engines, tolerances aren't as tight as a brand-new engine, and the thicker oil 'fills out' the space better. I'm no expert, so I'd wait until someone that actually knows about this to comment before making a decision, but I don't think it's something I'd do.
I've also heard it's worse to switch to synthetic on an engine that's always seen conventional than to just stick with conventional. Something about being bad for the seals. Again, I'm not an expert.