The XPS 13 does not use a quad core Skylake. It uses an i5-6200U or i7-6500U, both dual core. The XPS 15 uses a quad core; either an i5-6300HQ or i7-6700HQ. While the i5 in the 15" is a quad core, it is only capable of a single thread per core (4 Cores, 4 Threads), while the i7 is a 2 thread...