4.0 and 4.6 power difference.
 

I know the horsepower and torque difference, but anyone who has driven both. Is the difference anything worth writing about?

Nope, after all they have lost many of their ponies by now.

They're both underpowered.

There's actually a very noticable difference. I was pleasantly surprised that the 4.6 feels a lot stronger, gets up to speed with less throttle, and makes the disco feel comparatively peppy. It actually has enough power to chirp the tires when taking off, something my old 4.0 couldn't hope to do. It didn't seem to lose any low end when going to 32" tires either, it still feels a lot more powerful than my old 4.0.