All the time that I worked with Lightroom I saw one annoying problem: curves is very slow. I mean very slow response to my mouse move. If I'm using curve in Photoshop in file of any size time response between my mouse move and image is perfect it's real time. If I'm using curve in Bridge (open file in ACR of any version) time response also perfect. But in Lightroom using curves is much slower like "oh... may be I come back to old days with 486 PC" 🙂 I'm opening same images in ACR and Lightroom and in same windows size.
Also I should add that size of curve in Lightroom is smaller then in ACR so it's harder to make precise adjustments.