Imho the worst mountain is the downgrade going into Albuquerque. (And upgrade headed east)
A month ago I didn't find I-10 through Arizona / New Mexico noticeably better grade wise across the continental divide. Yes, the elevation is a bit lower on I-10
The forecast for the next couple days doesn't expect anything precipitation in the mountains on either route. Temps will drop into the upper/ mid-20s in western New Mexico on I-40 and mid-lows 30s on I-10 - in the forecasts are correct.
If I were heading to Las Vegas tomorrow from Dallas, I'd go I-40, but be ready to head south on I-25 at Albuquerque if the weather forecast changed.