3406c mech to 3406e,c15 swap.

Hey guys I have a 1994 t800h with a 3406c 3zj mechanical. It’s such a awesome engine but eventually I will need to do a rebuild and here’s where i need some answers. I want more power when I rebuild. This is a 425hp set at 475 but I run a dump truck and pup and am always pulling hills here in Kelowna and want more power. I am geared currently at 3:90 with a 18 spd. I am going to change gears soon to a 4:11 or 4:33 so that will definitely make a difference as well. I want a reliable rebuild and my hp goals are around 600-650. So I am wondering should I build a low compression 3zj with say the ipd steel 2 piece piston or swap in a 3406e, 6nz etc. I also have a brake saver on this truck FYI. Need some solid real world advice from those who possibly have Owned both engine types. I have only Driven a mechanical cat. Also would a 600hp mechanical pull as good power wise as a 600hp electronic engine. Or does the bigger cube electronic make that much of a difference... I’m looking to get a block next spring and slowly start building it myself and I can literally build whatever I want. Thanks for the help