I'm with you JoeD. Here is my current height measurement. It's about 5" I think with a 4x4 and 2x4 stacked. I'm pretty happy with it, but I did notice the bed is going to lose an inch and a half of depth, so I may jack the cab up another inch. I think it was skymangs plans that called for 6" between the top of the frame rail and the cross member of the cab. At first I thought that was crazy high, but now that everything is sitting on the frame, 6" sounds about right.
Oh, this height also gives me about 1/4" clearance with the trans. I'd have to do a trans tunnel if I move the engine back like you've suggested.