Do you happen to have an i3 or i7-based desktop PC? Or an i5/i7 laptop?
If you do, you can simulate those actually. Disable the extra cores (in case of desktop i7), and setup the maximum CPU clockspeed according to both the m3 and i5 specifications from Power Options in Windows.
From my experience, there wasn’t a huge difference between my i3 SP3 (i3-4020Y) and i5 SP4 (i5-6300U) in browsing, that much I can tell you. For your other tasks, its really down to your individual case.
And then theres the obvious storage difference, however from your comment here
If there was an m3 / 8gb / 256gb option, I would definitely go for that
It seems that you dont mind about the CPU performance all that much. In that case, its as simple as choosing the storage capacity. Remember, you can use a microSD card to expand the storage, though that portion of the storage wont be nearly as fast as the SSD. SanDisk got a 200 GB if i remember correctly.