Tyre Pressures (& sizes)

[Darkstar]

More of an idle musing than anything that I think will make a huge difference to my power output.
However, most of us do ride with different pressures in the front & rear tyres.

For a complicated set of reasons I also have different width tyres on the bike at the moment too (28 rear, 25 front) although this only apply a minority

For simplicity lets say that there are 85psi in the front & 65 in the rear - do I use the following in Isaac to set up the Crr:
28mm @ 75 psi (85+65/2) ?
Or 25mm @ 75?
Or go with the 60/40 split by weight i.e. 73psi for either the 28 or 25mm tyre?