generally 6.5" lifts run a 12" shocks. so you will probably be looking into a 14" travel shock.

but more importantly is you wont be getting much droop with shortarms and 8.5" of lift anyway, so the added shock length might not do you any good anyway.

but i must ask, why all the lift? what tires? what axles? whats it for? in many situations that much lift (especially with the shortarms) will hurt you offroad.

you would be surprised at how the added droop helps

 

Honestly I mostly do mudding off road. I dont do much trails. I just like lifted trucks. I am running stock axles I plan on 35 on road and 33 while off. I have two diff sets of rims and tires. As of now its 33 off road and some stock tires on road. Maybe it is not worth adding the extra lift.
Plus eventually I plan on building a Long Arm kit. I just need the time.