It's difficult to quantify, but I'd say the only thing I notice is battery life. On the x230, before the mods I've made to modernize it a bit more, the battery life was somewhere south of 4 hours.
With the Librem 13 I do get 6-10 hours depending on work load.
I'm probably not ready to replace it yet; it ends up being a terminal more than anything else and the performance is fine for where it's at. But... every now and then when I'm browsing, it'll slow to a crawl, and I pine for the fjords/something newer.
I've been holding back partly because it's still difficult to get more than 16GiB of RAM easily, but: is the Skylake-based Purism 13 a large or incremental step up in performance?