I gotta say, I think I might go back to the IG too. I was really disappointed in the mold change. They took the speed and revamped the mold to where it now feels like a IG Rad Pro or a IG Instinct. It has all those pointed traced angular edges and the head beam has a flat wide edge like the pure drive or the aero pro. They did away with the nice simple rounded off bevel beam of the IG and made it a little awkward to hold. I can't seem to get a comfortable grip with all the protrusions and it also doesn't help that it's thicker as well.
The thickness of the 99s is is something that I also didn't like. I can't wrap my hand around it with my off hand (something I like to do). Other than that, the spin is less pronunced. And with the new graphene the overall head shape is less oval and tear drop. They trimmed the head shape and made it more elongated similar to the prestige mp than the rounder traditional Speed. I think that's where the spin drop off comes apparent because the strings got tighter when it is squished in and the former rounder head allowed more string spacing, thus allowing more spin.
Not a fan of this model. Actually feels cheapish in production compared to the older IG. Didn't like the hexagonal protrusions of the Graphene illustrations as well. I am probably going to stock up on IG's before they get discontinued.