Why are you using 8ply board? Are you doing very large prints? (22x28 or larger).
Personally, I dont think 8ply mat is needed, unless you feel your work is not that good and you need to go overkill with matting/framing.
8ply board is very expensive, hard to store (takes up twice the amount of space and weight) and is VERY difficult to cut with a low quality cutter.
I use a higher end Logan cutter (BRAND NEW!) and to cut 8ply mat, you have to pass over at least 5 times. After doing that, your window is not very clean anymore.
I suggest staying with 4ply board. If you can afford to use 8ply, then just have a framer cut it for you.