Tori,
looks like you managed to get it. Overall, I like your images. They are relaxed and unposed (how do you pose a cat anyway) and I like the tight cropping on Skye's headshots especially.

What are you using for lighting? I noticed on the larger views that the images had a lot of noise so I assume you were shooting at a pretty high ISO.

The only other issue for me is that on the tortie kitten, the background is a bit busy. Also, that first image looks a bit soft to me (not quite in focus).

Shooting cats is very difficult. You do a very nice job of it. I tend to concentrate on dogs but my cat, OJ, will occasionally pose for me. So I appreciate your skills.

The lens seems sharp enough (what f-stop were these taken at?). If it works for you, there really isn't any reason to consider another lens unless you would benefit from IS. I suggest you rent one of the other lenses for a week and shoot with it to see whether it is an improvement in terms of your shooting style.

If you can provide more technical details on the images, I'd appreciate it.

Jim