A rough guide for suggested min/max tire section size based on rim width & diameter link:From some research I've done,
-If you want to stick with 19" track wheels, most aggressive I've seen is a 19x9 and 19x10.5 with 265/35-19 and 285/35-19 RE-71R, especially the GT4 crowd. Yes you can go 19x11 in the rear with around +45-50mm offsets, but there's not really any tire choices available to keep a similar diameter.
-If you want to go with 18" track wheels, lots of peeps are using 18x9 and 18x10-11 with 245-255/35-40 front tires, which have more tires available. As for the rear, choices are still quite good with 275-295s.
If the track you are running does not have much straightaways, dropping to a 35 series tires is a good way to go especially since your acceleration is increased.
Also, if your budget allows, I would suggest getting custom spec wheels like 18x9.5 and 18x10.5 to run Yokohama A052s in the size of 255/275. (Yes, a 9.5" width wheel can fit the front if you have around -3.0* of camber using top hats and control arms)