Some of the Thinkpads use a 16GB cache SSD, effectively turning the HDD into a hybrid drive. When I briefly had access to one, of course I reconfigured it as a plain SSD and ran some benchmarks on it.
CrystalDiskMark 1000 MB
Seq: 257.1 MB/s read, 52.33 MB/s write
512k: 196.6 MB/s read, 24.66 MB/s write
4k: 17.43 MB/s read, 3.867 MB/s write
4kQ32: 0.968 MB/s read, 2.668 MB/s write
So the speeds are pretty impressive for such a small SSD (4k speeds are substantially better than a HDD, which is about 1 MB/s for laptop HDDs). But even a budget full-sized SSD will put it to shame. If at all possible, go for the SSD + HDD combo.