This question really needs to be answered by you.
- What are you currently running
- Do they compress fully under articulation
- Do they extend fully under articulation
You don't want your shock to be your articulation bumpstop or limiter. I think these are the two most important items to determine the size shock you need. Assuming you have stock shock mounts you probably can inquire with the vendor of the shocks since they've been through it a thousand times. The main reason to not fully compress or extend the shock is it will eventually rip the tower off of your frame which can be bad. If you are not sure if your current shock is a bumpstop or limiter cycle your suspension with the shocks on until it is fully compressed and extended. Now take the shocks off and cycle the suspension again. If there is no change then your current shock size is fine, if you find that you fully extend or compress your shocks then you need to figure out which way you need to go. You might find that you do both, now you need to figure out if you need to move your bumpstop or put limiter straps on, or even may have to move the shock mounts to give you the optimum travel.