Comming in a bit late here but hey........... I owned both a trex 450xl with carbon eCCPM frame conversion and 100% alloy And an Ark X/MX400 with alloy frame eCCPM conversion with alloy head and tail etc. Both flew well but the X400 flew much much better than the trex more stable more responsive.
The trex cf frame used to distort with full power being applied where as the alloy X400 held solid with not a massive amount of difference in the weight

they both flew off the same radio with similar motor/ESC combos

Given the choice again It would be the X400 evertime. Its just nicer.

With that said I sold them both because small electric just didnt do it for me, nice to look at, but a bit small..........

See ya
Col.