Can I ask if you are looking at getting more braking power? If you are my advice would be to go for a big brake kit including new 4 or 6 pot calipers.It will be a big improvement over the standard set up and well worth the outlay.
I am not sure you will gain much by fitting bigger discs with the standard calipers.


This is what I have on my 2wd Saff and they work very well.Mine are the Hi-Spec kit but there are lots of different set-ups from various companies.