I purchased the MX83s, but didn't get a chance to ski them that much as I had an injury (not on the MX83s) and broke my humurus in 4 places. The good news is I was able to ski the end of the season, and used the MX83s several days (I didn't use them on poor snow condition days - I didn't want them beat up; I have other skis for those days). Normally I ski about 60 to 80 days per season, but because of my injury I only skied about 45 this past season.
I'm a solid level 7/8 recreational skier and I aspire to improve to a level 9/10. I ski Deer Valley & Canyons Resort in Park City UT.
I REALLY liked the Kastles on-piste. I didn't try them off-piste. On-piste & on bump runs they are amazing. I've never skied your reference ski (the IQ 76) so I can't give you a direct comparison. But the MX83s made the other skis in my quiver feel like minivans compared to the Kastle being a sports car.
In addition to the MX83s, my quiver contains the controversial Salomon BBRs, S7s, S3s, and older Apache Recons.
Regarding Dano T's comment that
"...The Kastle MX 83 I found to be more stable at speed but the ski does not tolerate anything but an aggressive weight forward hard charging stance. For me it is not a ski to get lazy with or be daydreaming..."
Well, I don't recall having that reaction. I don't recall the ski being unforgiving at all. I found it wonderfully precise and had a wonderful feel at both moderate speeds as well as hard charging (when conditions permit).
One thing I found interesting is the sound of the MX83 while skiing -- that's right -- the sound. Because of the hollow tip insert, as I skied down, I could hear the impact of the snow on the plastic insert, and it sounds different from the other skis in my quiver. It is hard to describe it - but I suggest demoing a pair to see if you like them.