X2 on the Hydro steering, good advice.
Issues could be 1) God forbid an accident occurred that was my fault and someone was injured badly. Now days things go to court way more than they used to and wouldn't an opposing lawyer love to find out the boat had a motor on it that exceeded the rating the boat had when it left the factory. I understand that Tracker would be involve in that scenario, but personally I wouldn't want any part of it. 2) Every blue book, repair manual and brochure lists the 08 Z6 at 130hp max. Having a 135 or 150 has a potential of being an issue with a prospective buyer down the road or at trade in time. 3) When I insured my boat with State Farm I remember them specifically asking me what the max HP on the boat was, I of course told them 130. I would certainly want to tell them I have a new larger motor and it might be an issue. Even if it wasn't I didn't want to risk a claim down the road where this would become a issue. IMO Insurance company's love to find reasons to deny claims.
I'm not saying any of these worst case scenarios are likely to happen. They were just things that crossed my mind when I was deciding if putting a 135 on my boat was the right thing to do. In the end I ended up moving up to a Z7.
With all due respect to the "Nitro Rep" the extra weight of the larger motor has little to do with solving the leaning issue. The different gearcase design of the 2.5L Opti (vs the gearcase design of the 1.5L Opti) is what solves the issue.
Please post your results, I'd really be interested to know how you like the 150 on your Z6, I think it will be a great rig.