I'm doing BOA conversion in my saph at mo and I've gone MT75 hybrid route for a few reasons really;
1. Mt75 hybrids are £350 less than converting a T5 (thats if you have one otherwise you got cost of a T5 box also).
2.T5 box's are good but do not like shift downs into 3rd (syncro's tend to fail).
3 For price it will cost to have T5 rebuilt (roughly £300-£400) I can get 4/5 standard Mt75 box's for the internals
4. Mt75 hybrid is a perfectly capable box to cope with BOA/BOB engine until you go twin turbo it and run medium to high psi
WES