You have the best answer right there, but if you can't get the fit sorted out before buying, you may just end up wasting, or being suboptimal with the $3-5k that you've got ready for the changeover.
( I listened to the bike shop & bought a QR in a Large. Exactly 52 weeks later after a Retul, I bought a P3 in an XL 61cm )

Until very recently, I have not been a Cervelo fan, but as you can see, I've recently got one.
If the sizing is right, I can't for the life of me see any reason to go past a P3, or even a P2

one of lifes treasures is buying a new bike.... enjoy the momet

pick the bike with the pretties paint job, the rest will fall in place =)

Have you tried checking ST for a fitter near you? How is your talon setup(saddle fore/aft, spacers, stem up or down)? Unfortunately the talon as a tweener bike isn't a great indication of what size or style of tri bike to go with.

Also meant to say, there are few bad bikes in that price point from the major players(cervelo, trek, spec, qr). After fit, Let ease of wrenching, integration, value, and of course you subjectivity guide you.