i've got 30mm of spacers in total on the back. Get em of badger5 fella on here with the longer bolts. good kit and price. do a searchy for him and the spacers = loads of posts
 
May as well get the 15mm spacers and longer bolts.
make a good improvement
 
Yeah, I wouldn't risk 8mm on standard bolts



... unless you're thinking of ending it all in spectacular fashion


Even with longer bolts, you'll have the same problem I have getting the wheels perfectly central cos you're effectively lifting the wheel off the spigot.

It's probably dangerous too, but I've not had any major issues