For subohm coils the recommended wattage is all bs, Ive used some that say 90-110 watts, but I always start out at 40w and then adjust up to the sweet spot.
If you’re getting burnt cotton taste could be dry cotton, try increasing PG percentage. I used to poke holes in the cotton with a needle or pin for the smok coils because they packed the cotton too tight
I haven’t had any issues with gti coils, typically 0.4 ohm, they last several weeks. That being said I don’t usually use very sweet juices and seldom go over 45w. AF is usually about 2/3 - 3/4 open.
I’d recommend the Vaporesso 0.40 (rated 50-60W more airflow) or 0.50 (rated 30-40W a little more restrictive Airflow) GTi Coil for running @ 40W. Now you can run 0.20 or 0.15 coils @ a lower wattage to gain more life out of the coil. I use the Voopoo PNP coils series 0.20 @40W and 0.60 coils @ 25W depending on the juice that I’m vaping.
If you are tasting burnt coils @40W with the 0.50 coils I’d try the 0.40coil @ 40W or try thinning your juice with a little more PG.