I've been keeping Red Iranians with my Angelfish for a couple months now and there has been no fighting, they stay out of each other's way. Some places I checked when doing my research say that the Red Rainbows need a lower temperature than angel but I have had no issues with my rainbows being in a tank at 78F. I wouldn't push it much warmer than that with them long term though.
p.s. My angel knows full well that the rainbows can outswim him come feeding time so to compensate, as soon as I open the lid he is up at the surface waiting for me to drop the food so he can get first dibs lol. I know every fish is different but mine is getting his food just fine for what it's worth!