Lot of varied opinions above, there are some other features not being considered.
Px:
- split bars easier to travel with
- more adjustable position up front
- ability to fit bladder in frame for more aero hydration
- ability to close arm positions tighter due to above ( I had BTA bottle and just wasnt the same nor as aero).
- said to have more comfort due to Beam
- more storage or more aero storage compared to P5d
P5d:
- lighter
- seat tube so some prefer the design
- perhaps handles better (in a triathlon does this really matter?)
If I were to switch to a P5d (and I do like the black/grey one), I'd lose:
- bladder aero hydration
- aero bottle on frame (as in standard bottle that is replaced at aid stations as frame is wider than P5d specifically for this)
- split bars ease of packing (not a big deal)
- better adjustments up front (minor disadvantage)
- add the storage solutions Yann made to pack the spares.
So I'd gain a lighter bike, but compromise on position, hydration and built in storage.
Really, its down to personal preference as the above are all minor and individual differences.
Personally, I love the bladder hydration and narrow aero position with straw that is now poss on Px.
The BTA was a pain, often ending with spilled drinks over basebars (when using torpedo) and also wider arm position for me.