I've never been a fan of the Raptor (my neighbor had one and had issues with support brackets and deck hangers)
The frame and build on the FasTrak is better.
But for mowing 6 acres I would be looking for something bigger, faster, stronger (my opinion)
I have a Hustler Super Z (35HP, 72" deck) for mowing 8 acres and it is an awesome/well built mower.