It is worth noting that the XPA-2 does double it's output into 4 ohms (250 wpc to 500 wpc), while the anthem only increases 50% (200 wpc to 300 wpc). So the XPA-2 does get closer to ideal amp performance than the Anthem does and this does generally indicated a better amp (or at least greater current reserves) to me.
The RPA-2 increases from 200 wpc to 350 FWIW. It's class H, which does run cooler and some people seem to prefer for some reason. It also has cool looking VU meters on the front.