The 340mm disc will work fine with the Golf R/R32/S3 caliper, as Radius not diameter is king in braking terms you are only 'losing' 2.5mm in effect

Neither the 345 or 340 will work with AP 4 pot calipers, but tbh it would be a travesty to hang APs over heavy single piece discs..
Audi R8 4 pot rear calipers with the correct brackets will work with the 345mm discs, but you'll need on average a 10mm spacer if you keep your standard wheels
