It doesn't make any difference as Lightroom does not use ACR. ACR is only used in Photoshop. You should use Lr 5.71 also with ACR 8.7.1
I'm confused... When you go to "Edit in Photoshop" from Lightroom doesn't it give a warning if Camera Raw doesn't match between LR and Photoshop? I've gotten a warning like this before...?
Yep - but Bob's still right.
You need version compatibility between ACR and Lr for the "Edit in Photoshop" function to work fully, but installation order is irrelevent as long as both are compatible the first time you use the function. ACR is for Photoshop only.
tthank you both for the info