I'm with you, aurdraco - the selection of wide-ass 17" tires is small, whereas 18" sizes are plentiful and the trend continues to go that way.
I have a set of 18x10 CCWs for my car, but they've basically only seen street driving (for the sake of testing fitment). I did about 3 laps on them at VIR last year before ignition issues ruined my weekend.
That's an 18x10", 7" BS with a 1/2" spacer (so 6.5" BS, or about +25mm offset), Fox length MM zero offset LCAs and MM K-member, '96+ spindles, etc etc. As you can see, I could go a bit thinner on the spacer, so maybe +30mm offset or so, which would make fender clearance a little easier. (I've got the Maier fenders, so clearance isn't an issue, but with stock fenders every bit you can gain will help with fitment.) I've got 275/35-18s on there. I could fit more, but those came off my CTS-V's track wheels, so they were readily available.
Based on your comments, it sounds like you want to go BIG, in which case I wonder if 10" is enough. I'm not sure what bigger take-off/scrub sizes are available, as I haven't really looked into it; I know there are plenty of 275/35s out there. If there's not much availability of tires wider than 275/35 (or getting the wider tires is cost prohibitive), then maybe 18x10" would meet your desires.