In video transcoding with Handbrake, the Intel Core i7-5500U in the LaVie-Z performs as expected. The 300MHz bump over the i5-5200U processors found in both the Dell XPS 13 and Intel NUC provides a bit of a bump in power, but doesn't touch the higher voltage i7-4870HQ found in the MSI GSS30.
In CineBench 11.5, we see the LaVie-Z within 10% of the GS30 in single-threaded performance. However in the multi-threaded test, the i7-5500U performance is more inline with the other dual-core hyperthreaded ULV parts, as opposed to the quad-core hyperthreaded i7-4870HQ.
The i7-5500U of the LaVie-Z provides a healthy bump in CPU arithmetic over the i5 ultrabook processors, but can't come close to matching the higher voltage i7-4870HQ.
3DMark Cloud Gate
Even though all LaVie-Z configurations feature i7 processors, it still doesn't mean that you'll be doing any serious gaming on this machine. With Intel HD 5500 graphics, you should expect the same GPU performance as you would out of any other modern ultrabook.
Since Lenovo decided to offer only one CPU option for the LaVie-Z laptops, I'm glad they went with the highest performance part for the given thermal constraints. While there may only be a 300MHz or so bump over the more mainstream ultrabook parts like the i5-5200U, the additional speed could help futureproof the machine a bit more without a large sacrifice in battery life.