IMO just judge the effect yourself when it's lowered. My VN is on ultra lows but only ended up with a few mill difference between each side. The 8" wide rims are under the guards but never rub over bumps or anything. Been going for years with the standard panhard rod.
Don't forget to do the front as well. Otherwise you'll get crap fuel economy from driving uphill all the time. And with ultra, ultra lows you won't see over the bonnet.
this guys on drugs for sure my mates got the cars on ultra on back n normal fronts and they see fine to ur info i will be doing front later on
mac the vn dont seam to have much of a problem with rubbing my mate lowerd his 8 onto superlows last week they look mint hasnt scrubed out on the gaurds but he has bottomed out up a few driveways due to large curbs... although i had my VR done professionally and tis just my oppinion pay the few extra dollars and have some1 do it for you its much better