So some SP4 m3 owners have uploaded geekbench results, here are the SP3 i5 vs SP4 m3 results:
Microsoft Corporation Surface Pro 3 vs Microsoft Corporation Surface Pro 4 - Geekbench Browser
SP4 i5 vs SP4 m3:
Microsoft Corporation Surface Pro 4 vs Microsoft Corporation Surface Pro 4 - Geekbench Browser
It stands up pretty well considering the TDP difference
TDP
SP3 i5 = 15w
SP4 m3 = 4.5 W (configurable down = 3.8W - configurable up = 7W)
SP4 i5 = 15w (configurable down 7.5W)
Geekbench 3 Score
SP3 i5 = 2701
SP4 m3 = 2420
SP4 i5 = 3082
Geekbench 3 Multicore Score
SP3 i5 = 5160
SP4 m3 = 4652
SP4 i5 = 6372
The previous results probably show the difference between the Integrated GPUs ... the SP3 i5 = Intel® HD Graphics 4400 vs the Intel HD 515 in the Sp4 m3. As you can see the SP4 i5 has a nice boost in performance over the last gen, especially in multi-core. I'd say the m3 stacks up quite well, the power to performance ratio is pretty phenomenal, will be very interesting to see gaming benchmarks as well as battery life results.