I tow my V210 loaded with gear and 4 people reasonable distaces behind a Mitsubishi Challenger (http://en.wikipedia.org/wiki/Mitsubishi_Challenger
) and while it does slow a reasonable amount up hills, on an hour long drive, it takes perhaps 10 minutes longer with the boat. New Zealand is typically pretty hilly also.
Ive got brakes on the trailer that work fine and if you dont drive like an idiot and leave the braking to the last minute it will drive fine and not push you around.
I think realistically if you think you need a 6.0 litre diesel turbo to tow a boat, there is something wrong.
Something a little more powerfull than the Challenger would be nice, but a 3.0 Diesel Turbo is more than enough in my experience to tow a wake boat and do it well. Ie (i know you cant get these in the US, but http://www.toyota.co.nz/NewVehicles/Models/Commercial/Hilux+4WD/SR5+TDi+4+Door+Double+Cab/3.0L/Auto/Overview/
Throw a transmission cooler on, and make sure its got regular fluid changes and i cant see why there would be any issues. Down here we regularly tow 2.5 tonne boats behind these up hills with no issue.
Just another opinion, that doesnt involve buying a 6.0 diesel, although a Touareg V10 would be my pick if money wasnt an object.