There's more to factor into that also, it's not just the engine.
Personally, I'd just rather do the upgrades on the truck I have now because of the other mods, the body style it is and the way I have it set-up. That's just me though.
You can never have enough and there's somebody else that always has more, so when are you happy?
For me, 400HP at the rear is more than plenty, Hell what I have now is more than I can reasonably use on the streets?
I don't race or street race, just as long as it sounds great and has great off-the-line torque, I'm happy.
I'm old though and I've learned the blessings of being content too. lol