I own the original Makos, Mako II and bought a pair of M7's (haven't worn those yet). I also briefly owned M8's, but they were D width which turned out to be too narrow even after baking so I sold them before even wearing them. Here are the key differences between the M7, M8 and Mako II:
M7 - EC50 Carbon Fiber Matrix (50% Fibre glass and 50% Carbon) with adaptive HDPE thermoplastic quarter. White felt tongue with an injected TPU metatarsal guard. Very thin ortholite footbed.
M8 - EC80 (20% Fibre Glass) with adaptive RX thermoplastic quarter panel. White felt tongue with an injected-plastic metatarsal guard (the metatarsal guard looks exactly the same as the one that was on the original Mako). Multi-Density ortholite footbed (slightly thicker than the footbed that comes with the M7).
Mako II - EC100 (100% Carbon) with adaptive RX thermoplastic quarter panel. White felt tongue with dual-density foam with a streamlined injected-plastic metatarsal guard (streamlined to allow for better forward flex). Multi-Density ortholite footbed (thicker than the one that comes with the M8).
So you can see that the M7 has the highest fibre glass content - that means they'll be slightly heavier and you'll lose a bit of energy transfer, but on the plus side Fibre glass can be less prone to cracking from hard shots than carbon; so they may be a little more durable. The HDPE thermoplastic may also be less responsive to heat than the adaptive RX (Easton called this an exclusive thermoplastic material) found in the M8 and Mako II. I have not baked the M7's I have yet; so I can't be certain that is the case. The metatarsal guard isn't as hard in the M7 as it is in the M8 and it's not streamlined like it is in the Mako II. The footbed is very thin in the M7, but it was also quite thin in the original Mako. The M8 footbed is a bit thicker and the Mako II is the thickest of all the footbeds.
They all have the extendon guard, are one piece boots and use the same holders and steel. The main difference is the fibre glass content as many others mentioned, but that's not the only difference. They all use wicking micro fibre liners, but the Mako II liner does seem like it'd probably be a bit more durable than the one found in the M7. I've used the Mako II since the summer (and that liner has shown better durability than the micro fibre liner used in the original Makos - I've had no issues with the Mako II liners, but had some noticeable wear with the originals after having used them for about the same amount of time), but haven't used the M7 at all; so I can't really say for sure.