By the by RX4's with new Shimano road is just for bling. If you want 4 pot with Shimano road you can use the MTB calipers as they are now cross compatible. Something like MT520 calipers are super cheap. For SRAM however it's your only option. Although for some reason and might be placebo my Rival hydro brakes got tons better when I bled them with Motul DOT5.1 vs the sram branded stuff.