With opt1: I'd double-check the wattage needed for the mx770's towers. It's not enough to really power the 880's but I'm not sure about the smaller cans. I'd personally do mid cabin over towers OR rear deck if you're doing it in stages. There's a massive "hole" in the middle of the boat in regards to sound so adding two speakers there is > than everything else, in my opinion. So I'd do that then towers OR deck if you can't do both.
Option 2: This is a pretty solid choice and will give up a ton of clear and loud sound. Towers are really designed for (anyone correct me if I'm wrong) towing people. So it's for the wake boards, tubers etc to have some tunes while they are out back. However, you can use them for whatever you want. If you plan to park the boat off of a sand bar/key/island the towers WILL project 80+ft if powered behind the boat. I dont have them myself (yet) but there was a boat with JL towers in the wake zone and it sounded like a moving concert behind him. It did offend a few people at the dock who had children and didn't prefer their type of music, etc. Logically, if you're someone who's going to hang out behind the boat by the swim deck (that's us usually) then towers are overkill. However, you wont have to upgrade any further and could technically skip the rear decks. PRO's - You'll have some high quality great sounding speakers you can hear while moving and from afar. CON's - $$$ as you'll need to buy the speakers, cans, and another amp plus wiring, distribution block, etc..etc..
I think this is the best starting point for non-wake/towing cruisers.
Option 3: You can't do wrong with this is money isn't an object. And if its not, I'd considering splurging on the 8.8 towers. The m8/800 for the 8 650's and m400 for the towers.
One other thing to consider, you could also (if you want to go big instead of going home) is:
Option 4: Instead of 650's, do 770's in the cabin x6 (you have to slightly enlarge the factory holes but otherwise no issue)
Option 5: 4 650's in the factory spots and 2 770's in the mid cabin (I'm 90% sure they fit there but I'd dig around to verify)
Option 6: 6 650's inside, 2 770's swim deck - This seems to be a fairly popular option.
Add in towers as you wish with those option. Both the m800 and m400 still work.
Last thing - As much as I wanted to go 7.7's eveywhere, for the money odin@earmark said for the money the 6.5's where a really solid deal/setup. Bolt right into the factory holes (still have to cut mid cabin and rear if wanted) but otherwise they are near half the cost PER set x "X" number of sets of speakers. I think my boat sounds awesome now and I can always upgrade later (maybe swap in 7.7's in the mid or rear deck when I add them) and see the difference. Just something else to think about. You really wont hear the speaker on the bow from mid cabin back so if you're not really up there often then maybe 7.7's are overkill. IF you like to measure twice and cut once then splurge away!
Also: The sub (you can go IB or sealed etc) even a solo one, really completes the sound. I can't believe how well you can hear it even WOT, again in the mid-cabin towards the stern. If I sit in the transom area I can barely hear it even while parked unless it's cranked up to give an idea. Not complaining but its amazing how the sounds changes based on wind (open air environment, right?) and probably because its installed very low and the sound does travel well over the hump there to the back of the boat. Word on the street is the 8.8 towers are like subs or maybe are subs and you get some solid bass from them from what I've read so far.
I'm assume doing a Wetsounds setup would be similar but I can't confirm.