If i'm running 5mm spacers in the rear do I need to use longer studs or can I just use the existing ones?

I'm under the impression that 5mm is ok.

Thanks

 

You would need longer lugs.

 

If you go this route, make sure you torque your lug nuts at least once a month, I had spacers with longer than stock studs the studs broke on me (nearly lost wheels in the process), I wouldn't ever recommend using spacers after this....