Taking a look at the Surface Pro 3 and what we should see inside the Surface Pro 4:
- Surface Pro 3 Core i3 4020Y: 1.5GHz dual-core, no turbo, GT2 Gen 7.5 iGPU.
- Surface Pro 4 Core i3 should receive either Core-M (not likely according to leaks) or Core i3 6100U : 2.3GHz dual-core, better IPC, no Turbo, GT2 Gen 9 iGPU.
- Surface Pro 3 Core i5 4300U: 1.9GHz dual-core, 2.9GHz turbo, GT2 Gen 7.5 iGPU.
- Surface Pro 4 Core i5 6300U : 2.4GHz dual-core, 3.0GHz Turbo, GT2 Gen 9 iGPU.
- Surface Pro 3 Core i7 4650U: 1.9GHz dual-core, 2.9GHz turbo, GT3 Gen 7.5 iGPU.
- Surface Pro 4 Core i7 should receive either Skylake-U GT3e (real Iris Pro with eDRAM) or Core i7 6600U : 2.6GHz dual-core, 3.4GHz Turbo, GT2 Gen 9 iGPU.
Note that a Skylake GT2 Gen 9 iGPU should easily be faster than Haswell's GT3 Gen 7.5 iGPU at 15W, but I'm hoping they will postpone the Core i7 model or put the Core i7 6600U in there and include Skylake-U GT3e SKU as an option later on.