Dunno which is stronger TBH but for that box, you can either try and source an original dccd wiring loom, relays, switches, display, and control module, or you can get an aftermarket setup such as Neetronics or DCCD Pro. The latter is the cheaper and better option for a DCCD retrofit rather than sourcing original parts (Its on my to-do list)
I think someone on
here was selling a Neetronics for £150 which is a bloody bargain !
If you fit the box with no controller, you will just end up with about 65% of the power going to the back so it doesnt all have to be done at once. You will be putting more stress on your rear diff and drive shafts though so if any are near failure but not showing signs of failure just yet, they may let go quicker with the extra power they are handling.
The rear diff just has to be the same ratio so it doesnt matter if you dont get one with the box, as long as you have the same ratio on your current rear diff, or source another
As for gear ratio's. maybe compare your existing and new box codes on the
SPDA transmission chart