I would start at 50-ish, let it stay for a week or so, and see how much chlorine you lose in a given day. Then bump it up to 60-70, and see if your daily chlorine loss lowers. If so, then you can stay there or maybe bump it up just a little more. If not, then it's not hard to backwash out 10-20 ppm CYA to get it back down to the 50 range.

I'm close to Shreveport LA, and I keep mine in the 80-90 ppm range, but my pool is in full sun all day. I find that with a CYA of 40-50, I lose approx. 4-5 ppm chlorine in a day. At 80-90, that daily loss drops to around 2 ppm.

Just remember that as you raise your CYA, you must also raise your minimum chlorine levels (see the link to the best guess chlorine chart in my sig). I know it seems like you're still using more chlorine, but once you get to your required baseline, it still uses less to replace 2 ppm daily than it does to replace 4 ppm.