Do the calculations...

http://www.superjamie.net/garage/tire.xls

I think the stock offset on libs are +50 or +55... Ive got 18x7 with +45 offset with 215/40 tyres and they dont rub... If the offset on the KSpeeds are lower than +45 dont get em...

my offset is +45 and i had to roll my guards to get a 17x7 under there, the tire still rubs right up deep inside the wheel arc but thats only when i'm drivin pretty hard and get to a corner that also has a dip or lots of camber.

if you want 7.5 under there (which is illegally wide in aus btw, 7 is max) your offset will need to be pretty close to 55