Differences between Intel i7 "M" and "U" series

What are differences between 4th-gen i7 M and U processors?

I know about:

• core voltage
• TDP
• socket
• price

But is there something more? Some differences like slower cache, reduced instruction set?

So, for comparison - I took two 2-core Haswell i7 processors with... same numbers - 4600M and 4600U. It may be wrong, but I couldn't find pair of M and U processors with same cache and similar clocks.

U-series is very diffrent. It's not just M-series with lower core voltage.

• There is no PCI-express 3.0 support
• PCI-express (2.0) only in 4x1, 2x4 modes (no 1x16)
• USB and SATA controller is built-in
• diffrent memory controller (supports low-power memory)
• in some low-power devices with U-series CPU may slow down under long and heavy load (throttling, less Turbo etc.)

These are only few differences. There is a lot more, but my question seem to be not popular, so there is no reason to list them all.

My final verdict about performance differences between M and U series is:

U-series performance (per 1GHz) is same as M-series, but PCI-e limits may reduce system performance if you want to use GPU somehow (3d or as coprocessor).