Neither an Evo or Sti will trouble a GTR Nissan. Unbelievable grip for a 1.8 tonne car with blink and you'll miss it acceleration. Mucho respeito for that monster.
But the GTR aerodynamically at least, is pretty basic.
For a grip/aero combo you will need something that was designed to race first, then reproduced for homologation purposes.
2 cars stand out, those being the Porsche GT1 and the Mercedes CLK-GTR.
Both these did however suffer flip incidents in races.
But for production purposes the cars were raised slightly higher(tyres)and given more stable front end bias.
Both remained millimeters off the ground though, and sported massive functional diffusers, racing floor as well as rear wings and profiled front splitters.
They were practically unchanged from the actual race cars apart from tyres.
I reckon they'd qualify for aero and grip when you consider the race spec were lapping the silverstone race track in 1m:38 in 1998 when F1 was doing 1m:23 with 200bhp more.