Erm I did, They actually come out past the arches by 5mm.
but doesnt help when the new arches are alot wider than usual
Sorry, mate, I don't understand. The wheels when fitted come out past the arches or sit inside the arches by 5mm? Spacers will only push them out further AFAIK.
Lol, I need them to sit out further, by quite a bit lol, I am getting a new bodykit and the wheels will look sunk in
OK, I think I've got this! Without the body kit they sit outside the arches by 5mm but with the kit on they sit too far inside.
You want hubcentric spacers and I think Eibach do some which should be decent quality.
As for downsides, IIRC they can cause undue wear but I can't remember if its driveshafts or hubs. The bigger the spacer the worse it is. Don't know if that will be magnified as your offsets must already be pretty aggressive.
HTH