questions bout spec per tank?

I'm not sure entirely what you're asking but Mutilate builds are generally superior in largely single target encounters where Combat is more versatile and better for fights with specific dps burns are necessary or target changing is frequent. As for raid utility and bear tank synergy; mutilate used to be great with a bear tank because rupture was a constant part of the rotation, however rupture does no scale well so it is usually eliminated from rotations in both specs once gear level gets over 245. Combat builds actually provide a little more raid synergy now with the Savage Combat talents.
If you do go Mute, the rotation is fairly simple these days. Keep Hunger for Blood up at all times (open with garrote if you can start in stealth to initiate the bleed - otherwise a warrior or druid will usually put up a bleed within seconds). After you get your first combo points (only a couple will do) start a cheap Slice and Dice, Mutilate, Envenom. The first envenom does not require many combo points as you just want to refresh you Slice and Dice to full duration and apply the Master Poisoner effect of increasing your chances to apply deadly poison. After that you just mutilate to 4-5 combo points and envenom on repeat. Just be mindful not to "step on" the Master poisoner effect which last 6 seconds and keep your hunger for blood up.
As for stacking Attack Power - armor pen is a horrible stat for Mute because far more of your damage in this spec is poison damage, not physical damage. A mute build with tons of Armor Pen will not be successful. While Armor Pen stacking is optimal for combat specs, Attack Power is still a valuable stat in combat so if you are going to be switching between the two specs and do not have the luxury of different armor sets for each build Attack Power stacking is the reasonable choice.

I hope this helped, I'm not sure if I really answered your question so let me know if you have further questions.