The attached screenshot may be of interest. I routinely conduct performance tests for comparison purposes (initially going back to LR3 using Canon 5DII files, but more recently updating to 5DIII files). The tests involve tasks that I can objectively time, specifically 1:1 preview generation and exporting. I've just updated my chart with a direct comparison of LR5.7.1 and LRCC, and the tests are run on both my Mac and Windows systems, with the latter being run twice to compare the effect of having hyper-threading enabled/disabled.
A couple of observations:
1. These are objective timings, i.e. it's pretty safe to draw conclusions from the results. But how Lightroom performs in daily use is much more difficult to assess, and for sure I've already noted that on the Windows platform LRCC takes several seconds longer than LR5.7 to start, but other than that I'd be hard pressed to notice any difference between the two. With the GPU enabled I definitely see a tiny bit more smoothness when pushing sliders around, but the difference is so small it really makes no difference.
But I'm not a power user, so I very rarely run into performance problems that start to occur in longer sessions....I do sometimes have keyword panel slowdowns in an elongated session, but that occurs using both versions.
2. Looking at the specifics of the timings, pay no attention to the fact that on OSX everything is significantly faster than the same task on Windows....the Mac system (late 2013 model MBP) is 4 years younger than the Windows desktop system, so I expected that major performance boost (if I hadn't seen it I'd have wanted my money back!). So looking beyond that it's interesting, to me at least, to note that LRCC on my MBP is a little bit faster than LR5.7 in rendering 1:1 previews, but consistently a little bit slower than 5.7 on the Windows system. I think I'll try mentioning that to the Adobe team.
3. The Export timings do show a significant performance increase using LRCC versus LR5.7, on both platforms. This is as expected due to the engineering enhancements that Adobe made to the Export process.
4. Windows users might be interested to note how little difference there seems to be whether hyper-threading is enabled or not.