Jonny,
In all honestly, if I was doing it again, I would have the HiSpec on the rear - I still may as I think the Wilwood may be marginal. I still need to set it up properly and see if it will grip enough. The other option is maybe to make new cam arms for it that will give greater leverage; this will work on my 17s but wouldn't if you go 15 (see my build thread, the arms just clear on a 15 wheel). The Hi Spec come off radially, so you can push the caliper out further for a bigger disc.
Being a bit OCD at times, I would have HiSpec on the front as well, as they get good reviews and then you can match front. I believe also you can pay a little bit extra not have their logo if you don't want it.