When you say "chain rub", are you talking about the front derailleur rubbing on the chain when you're in the big-big or small-small combo? If so, a new crank isn't going to solve this problem. As mstateglfr mentioned, this is a derailleur adjustment issue. You should be able to adjust the FD so that it doesn't rub on either end of the spectrum.
Unless there is something specific about the Praxis crank that you don't like, I'm not sure there's anything to be gained from swapping it to an Ultegra crank. Your bike has a BB86 pressfit bottom bracket, so the Shimano crank should work. I'd just run whichever crank gives you the best gearing - with either you'll need to adjust your FD so that it doesn't rub.