I'm a bit late to this discussion, but did ski the CX80 and AC50 last year, and have notes, so here goes.
Me: 5'-8" 155 lbs. Ski on Head XRC1100sw in a 170 at Bear Valley CA.
Overall, I liked the Rossignol way better than the Volkl. Main issue was versatility. If you want to rail GS turns of the exact same radius all day in anything but powder (yep, for me these will bust crud, crust, cr*p, etc no problem) with that "locked in" feel, go with the AC50 no question. If you want to do just about anything else, go with the Rossi.
Volkl AC50, 170cm
Bear Boogie, Monte, Tigger,
Possibly the first ski I've ever ridden >70 mm underfoot. Felt very wide, even tippy. Very conscious of effort to get up and “balance” on edge . Once I figured out how to do this, it was a breeze to set them on edge and the skis would carve deeply and effortlessly. VERY solid and stable in a turn, no apparent speed limit (I was not pushing these too hard, but they clearly were no where near their limit). Skis wanted to be ridden middle-back: I was having trouble with initiation and noticed I was washing through some turns before I realized I was jumping on the tips too hard (I do tend to lean forward too much). Once I relaxed, kept weight centered, and focused on edge angle, out went the train tracks behind. I could sit back as far as my quads would let me – edge behind felt limitless, and let me feel full length of the ski (note: I did ask for tech to check boot sole mark, and they said I was set dead on the mark). The only downside is that they seemed one-dimensional: it was difficult to get different radius turns. This may be a function of my lack of experience with wide skis, especially on ice. I did get them on a sunny slope with some soft cover, but had trouble getting short turns out of them.
Rossi Classic 80 (CX80), 180cm 180cm: R18.7, SC124/80/112
Porridge, Snow Valley, Grizz Face
After finding the CR70 in a 175 too long, I was hesitant to take this out, but it was clear who ever had the 170 was not bringing it back, so I decided to give it a go. Tech said that this ski liked to be skied long. After my first run, a moderately steep groomed bowl, a friend came up and said, “OMG, you were FLYING”. I had taken a couple of slow speed warm ups, and then let them run through some wide sweeping turns. I knew I was going pretty fast, but they felt very calm. Unfortunately, the ice was thawing out, so getting a good hard-snow comparison was not likely. What to do? Head for something steep and wide-open. The trip over was a rolling groomer, and these skis rolled it like I was on a SG course – gotta be careful of the speed on these things, because I found air on a couple of small knolls that came up way faster than I had expected. Target slope was re-frozen mashed potatoes. They sliced right through, even kept auto-pilot like steering when I flailed about. Bomber? B-52! Back up top, I met up with another buddy, who convinced me to take them down the moguled lift-line route. Amazingly, these things rocked! Big plus is that they are soft enough to negotiate bumps. Soft flex also allows lighter skier to have fun with different radius turns. Tons of confidence. Do I want to try the 170? You bet, but I'm seriously considering the 180.