what is better, a p2k with durace or p3 with ultegra?
Purely between those two choices, I’d probably do the P3 with Ultegra.
To me, it seems that a P2K with Ultegra and a P3 with DA go “better” together. I know that price wise, that probably isn’t an option. But the best frame and the best components seem to fit together more nicely. shrug 
A more expensive brake, crank etc. doesn’t make any real difference. Ultegra does the job. It’s the frame (and wheels) that mattes.
(Had Ultegra for 4 years, functioned OK, no problems exept the poor plastic crap they have inside the left hand brake/gear shifter. But of course - Campa is much better, more solid, shifts better, better feeling - but it don’t make me faster.)
Actually, the best choice for that amount of money would be a P2K with Ultegra and a Renn disk.
I agree, I am enjoying my new (to me at least) P2K with Ultegra. I’ve ridden Dura-Ace, and didn’t notice a performance difference. Unless you like shiny components, go with the Ultegra.
Chris
I agree with John. P2K with Ultegra and a Renn disc/front aero wheel. Most bang for the buck.