Thanks for this and your many other helpful posts I've read while researching & prepping this car!
Here's what I found (thanks, tirerack!):
245/35-19 PS2: load index 93(XL) @ 33 PSI = 1178
265/35-19 PS2: load index 98(XL) @ 35 PSI = 1430
275/35-18: load index 95(SL) @ 26/27 PSI = 1164/1199
275/35-18: load index 95(SL) @ 33/34 PSI = 1407/1443
Note that the Dunlop Direzza Sport Z1 Star Spec have SL load range, whereas the Michelin Pilot Sport PS2 have XL load range. Therefore, I used your chart to get the load for the PS2's, but the chart I posted later in that thread to find the PSI for the SS.
So, it looks like I should be running 26/34 F/R on my Star Spec square setup. I'm a bit surprised at the bias. I think I'll actually do something closer to 29/32, since I'm guessing some of that bias was to give the front tires a larger contact patch for a bit more bite. Switching to 275's should reduce the need for that and I wouldn't mind a slightly larger contact patch in the rear.
I'll also be keeping an eye on how the tread wears.