Dean, actually a good and cheap "half way" measure is to get the standard diff plated.

I once launched my old Saph, it went well up to about 50 MPH and then there was a loud knocking noise. The front diff casing had cracked in half!!!

Sent the unit to Steve Scott (A1 Rally Sport)....He then supplied me with another diff (standard internals) but a plated version - i.e. a specially made stainless steel plate that both halves of the casing bolts through (about 6 to 8 mm thick). This is a good low cost way to strengten the standard front diff.............About £ 60.00 for the s/steel plate IIRC.