89lude I run Fed RSR 205/50/16 at the track (Done probably close to 500 laps at 7 track days) and they are a simlar tread wear to your RT615. Now I've played with everything from as high as 45 down 32 and I've come up with 38psi for the front 36psi for the rear. The RSR do have a stiff side wall but seeing as your 45 profile is a little less I'd expect you best pressure wont be far off this.

Randy 40psi is gunna be too high for the RSR I reckon, I set my best times when track temp got to 29C back in Feb, was running 38F/36R. keep in mind my FD1 is fairly front heavy with 60/40 weight bias.