I have both: a 5mm Celestron X-Cel ED2 (similar to the Orion Epic ED2's) and a 6mm TV Radian. Had a shootout on Mars with them the other night and here is the verdict. Seeing was pretty stable and I got good views of the north and south polar ice caps and some major surface markings. Both are very similar on axis and both gave very sharp views of the planet. Light throughput was similar. However it pains me to say this but the X-Cel gave a slightly more natural tone to the planet. Views were warmer in the Radian. Off axis the Radian was sharp to the edge and exhibited no flares (good if you are using an alt-az scope). By contrast the X-Cel was noticeably softer at the edges and when Mars was placed outside the FOV, there was a minor flare (nothing major just annoying).
And there you go
Darren