The GT4e will have 72 execution units (EUs), 50 percent more than the best Broadwell IGP, so combined with architectural enhancements the GT4e integrated graphics promise a big performance gain vs Broadwell. The Skylake GT3e on the other hand has 48 execution units, the same as Broadwell, so gains will be limited to architecture enhancements. Skylake GT3e has 64MB eDRAM and will be used in "U" series CPUs.
GT2 graphics will be the most common type in the Skylake lineup, it has 24 execution units and will be available in desktop LGA1151 CPUs, "U" 15W SoCs, "Y" SoCs and "H" series processors.
GT1.5 has 18 execution units and will go into dual-core LGA1151 CPUs, while the lowest-end GT1 graphics has 12 EUs and will be used in dual-core LGA1151 CPUs as well as in some "U" series CPUs with 15W TD.