Whilst there's 5% off summer tyres at mytyres these are as cheap as anywhere, but there are 4/5 variants for 225/45 R17 225/45 R17 91V with rim protection ridge (FSL) E rated for fuel 225/45 ZR17 (91Y) with rim protection ridge (FSL) E rated for fuel 225/45 ZR17 (94Y) XL with rim protection ridge (FSL) C rated for fuel 225/45 ZR17 94W XL with rim protection ridge (FSL) C rated for fuel (For Porsche) 225/45 ZR17 94Y XL C rated for fuel (possibly discontinued 11 left +£10 each) Primary choice would be (3), but I'm not sure whether to consider (4) or (1&2) And to confuse matters further I'm considering 3 or 4 on the front with 2s on the rear so that they could be swapped front to back for comfort or cornering, but not sure if it would be noticeable or a good idea with the 2s being E compared to C for rolling resistance.
An 8l S3 standard tyre rating should be 91Y - load rating meaning 615kg max per tyre A 94Y is rated for 55kg more load per tyre at 670kg. I'd probably just go for the 91Y's all round as I doubt you will be running heavy weights and they will probably have a more compliant side wall.