As long as you rev match, there's absolutely nothing wrong with downshifting to 1st at speed (just be sure to get on the gas right away or else you'll be jerking around because of engine braking). The "never shift into first while moving" is an old wives' tale. It's a good rule of thumb for people who are novices at stick.

 

sometimes when i have to go up a steep hill i need to shift into first or i will climb the hill really slowly in 2nd