As I see it (for what that's worth), you've got three options if you're really concerned with the basic 818's unsprung weight (esp. up front):
- The Easy Route: 2-pc rotors, lighter calipers (ala Wilwood), and the lightest wheel/tire combo you can find (likely 17" dia. w/ 205 or 215 race rubber)
- The Bucks Route: one of those defibrillator-requiring Subie-motorsports uprights
- The Engineers Route: fabricate your own while figuring out the suspension geometry anew

The trouble with looking to "common" routes taken by sports racers and such is that those uprights are (a) often made for insanely light cars...think "half-an-818" and (b) more importantly made to work with very differently configured upper and lower A-arms. If you used one of those (assuming it was strong enough and fabb'd your own lower arm or made it work with the OEM lower) you're still looking at having to use an adapter similar to the one FFR came up with for the Subaru spindle so that it'll mate with the geometry intended by the upper A-arm. Unless...unless you fabricate a completely new upper A-arm and likely re-mounted it in the frame.

I think this is what RM1SepEx was getting at; this is a very tall order and the reason I call it the engineer's route. You're basically reworking the entire front suspension. Any effort to preserve what FFR did is going to land you in one of the first two options.

Personally, I'm with Slatt; I'd also really like to get the stronger/non-press-in bearings and 5x114.3 bolt pattern. I thought there was a thread somewhere with folks discussing a spline count concern with the axles and STi hubs... Anyone? If FFR doesn't come up with a solution here, I fear custom half-shafts are in my future because I want these two of the three Slatt laid out. [Oh hell sure, not like my budget isn't thoroughly trashed already.]

Best,
-j