410 vs 450 degrees for flat iron?

I have a couple of flat irons now that max out at 410 farenheit. I have thick, very curly hair and always use them at the max setting. I recently have been shopping around for new ones and have found some that go up to 450 farenheit. My main concern is speed . . . when I use the 410 degree I still have to make several passes through each section of hair to get it straight. I know that 450 will be more likely to damage my hair, but I use heat protectant and overall have pretty resilient hair.

So, does anyone know if the extra 40 degrees will make an appreciable difference with regards to speed?

I know nothing about it, but since paper burns at 451F, 450F seems awfully hot. Not sure how much, if any, protection a “heat protectant” affords.