Re: 6" rod
The larger issue is that unless you destroke, you have to push the pin up in the piston to accommodate the rod. This forces the ring pack to move up and tighter together, which gives you less material in the crown area. (unless you have a tall-deck block, of course)
Turbo motors make a lot of heat, so you want more crown thickness.
This isn't something I'd consider to be a terribly good idea for a street motor. If it's a race motor that you don't mind pulling apart periodically, you could play with it.
I was always curious about making a long rod/short rod motor, with a custom intake...