I had this dilemma recently too. I’ve cut and pasted my contribution to a roadie forum on a very similar thread below…in a nutshell, I didn’t feel ‘inspired’ by the PX, but then everyone’s different, you might love it.
“I had an alu Airborne Thunderbolt until recently – nice 9 speed Campag Veloce (9-10 years old) – quite a harsh ride though so wanted a smoother, more relaxed ride.
Looked at a Defy Composite which was lovely but £1600. Tried a PX Pro in Rotherham – yes it’s a lot of kit on a carbon frame but didn’t feel better than the Airborne TBH so went off the idea straight away – it felt a bit ‘cheap’. Then I noticed a Cube Agree Pro 2013 on Chain Reaction – £1400 down to £930! Tried one and that swung it. I’m no expert but my first ride had me smiling and I have no regrets whatsoever. Cuts out so much road ‘noise’ and feels almost floaty smooth. Quite a relaxed geometry (short TT and higher front end) with decent kit – Aksiums, 105, Ultegra (rear mech) 10 speed groupset, Easton finishing kit. Ok – the brakes and c/set are cheaper but absolutely fine and can be upgraded when they wear out. Respectable weight, stiff and looks bloody ace! Everyone has different opinions/experience etc but I am very happy with it – you CAN get a half decent carbon bike for under a grand by looking at last year’s bikes if you’re not bothered about the latest kit. Go for the Cube (FWIW I got the 58cm an I am 6′ – it’s spot-on size wise)”
Yes the PX has better kit, but the Cube feels like a better bike – to me anyway 🙂
EDIT: Brant – has the spec changed as I’m pretty sure the one I tried less than 2 months ago in Rotherham was 10 speed Ultegra and a downgraded c/set?? The RT57 had full 11 speed Ultegra.