My 395's (actually 15.5's) came on 50-50 offset wheels, probably from a M1076 trailer. The advantage to this is this offset means you don't have to worry about your steering hitting the tires.
I have a full set for sale (dirt cheap), with adapter plates but shipping would be steep to LA.
I don't think you need hydraulic steering, once the truck is moving at any speed you can turn the wheel - I have a tight driveway, in a city, on a one-way street, getting in/out was a pain but far from impossible. If you plan on parallel parking the truck I could see the advantage though, or if you off road a lot. It is heavier to turn, I really noticed that when I switched back to dualies.
While my XL's are rated at 55, I frequently drove them around 60 and, maybe 65 downhill with a tailwind. My thoughts on this are that I wasn't carrying a load and most safety ratings in the US have a margin of error. As for your speed, well, a 46" tire is 15% bigger than a 40" tire, so you can go 15% faster. This is a bit simplistic because nothing is exact, but you should be able to do 60 with the 46" tires, though it might take you a while to get to that speed as long as you're not going up hill.
Oh, and I flipped the castor shim. That really seemed to take the edge off of highway driving with the bigger tires. Before it seemed like I was always fighting to keep the truck in its lane. If you don't hardly do much highway driving, I wouldn't worry about this - it's really noticeable at higher speeds.
