Have you looked at the Vredestein Ultrac Sessanta? There are a few members running them and they are available in both 275/40-17 and 315/35/-17.
A fellow club member is running them on his 01 Lingenfelter twin-turbo coupe and really likes them. This
company has them but they are in SoCal so shipping to you would be a chunk of money.
According to the Vredestein website, there is a dealer in Peabody that carries them.
Direct Tire and Auto Service
231 Andover Street Rt 114
Peabody MA 01960
Telephone: (978) 532 5400
Do a search on Vredestein and there could be some online sources besides the CA company.
One downside to these tires is that they are narrower than other tires especially in the 315/35 size. But from what I have heard so is the Sumi tire at least compared to the GS-D3