LaRoche isnt coming to Boston. The Sox dealt him for Kotchmann for a reason. They value his defense and his ability to make contact over LaRoche's power capability.
Beltre would be an interesting player. He was absolutely terrible last season, so park effect or not, he really, really sucked. Now, one of his balls got smashed, so mulligans are possible when you become a uni-ball. With the move to Fenway, and surrounded by good hitters, he probably cracks the .800OPS mark. That being said, he needs to make a massive improvement over last season to approach that. Also, the sox will likely crack the luxury tax with a Beltre signing, so that might not be in the cards.