I know the topic has deviated, but as for Ford or Chevy, the one nice thing about the venerable V10 is that it has room to mod it. I have read about Banks mods such as the water/methanol cooling system which without any additional modding, can add 175 HP. There are also high volume, low boost twin turbo kits available (which are mainly to help keep the air coming in at higher elevations), as well as tunes.
Of course, all of this will kill an engine warranty dead, but it makes for an interesting array of options.
Banks especially, since they have a nice lineup of options for Ford V-10 motorhomes. I like the water/methanol option combined with a tuner for starters. The added 343 lb/ft of torque and 100+ horsepower can't hurt. Of course, no clue what it does to the engine long term, but I've read about E-350/E-450 owners with these kits, using them with no ill effects years down the road. You won't be able to win races, but it will definitely help on hills and such.