I think I can share some insight on the skis, and from a perspective somewhat close to yours. I purchased the RTM 81 last year and skied and taught skiing on them all winter. As a frontside carver, the RTM 81 is the best ski I have ever had. It is a very versatile ski, it does all turn sizes well, and comes around quickly. It loves doing short turns.. Although it is considered to be a rockered ski, mine are slightly cambered in the middle, with early rise tip and tail rocker. With the steel reinforcement, it skis a lot like a cambered ski. It is very precise and rewards good technique, and tolerates less than perfect. Like all Volkl Skis, it has great snow feel and gives you good feedback. I think that if you like your AC30's you will love the RTM 81 and transition quickly. At your skill level, you would have no trouble handling it. As for length, I had the same debate at the ski shop. I've been skiing 170's for quite some time and that has been a good length for me. (5' 11", 170 lbs) I ended up on the 170's, but I think I could have skied the 177's quite happily as well.
But I mainly used it on the groomers. When the snow got 4 inches or more deep, I pull out my old rockered Volkl Bridges. At 95 mm in the waist, it just does better in the powder. The RTM 81 is ok in powder, but that is not its strong suit by way of comparison to wider new skis.
I have several friends on the ski school on the RTM 84's. They absolutely love them, and ski well on them. That extra 3 mm would make them a better powder ski than the 81's.
If you are a Volkl loyalist, have you given thought to the Kendo? At 89 mm. in the waist, they may be a happier medium than the others. And this is not considered a wide ski anymore. Moreover, skis of this width are far more maneuverable and versatile than skis of even 5 years ago.
Visit a few ski shops and have this conversation with someone knowledgeable who seems to care about putting you on a ski that you will want to be on.
There are lots of good skis out there besides Volkl too.