If the MP10 will work for the thickness of your glass, and you will NEVER get a second mp40 or upgrade to a tank with glass thicker than 3/8inch I would go for the MP10s.
At minimum I assume 1/2" glass due to how much water it can hold. Like many have said, the MP10s are rated 3/8" thick but plenty of people have said they will work on 1/2" but to be safe use the cable tie/mount kit to prevent it from getting knocked off. It would be a nice combo IMO as you can have one on the side and the other on the back wall, have them alternate so the waves clash.
Safe bet would be the MP40, many as well have said one is more then enough for their tanks. Maybe an MP40/MP10 combo?
While building Tank #1, most people don't think about a future upgrade to Tank #2 (or more.) When I building my 60 cube, I bought an MP10 but found it wasn't enough so I bought another MP10. I now have a 120 and those two MP10 weren't enough - I've bought two MP40's. With four MP's in the tank (but usually not all on at the same time), I have LOTS of flow.
I say go with the MP40 now ... you will have a lot of flow today and be better prepared for tomorrow.
This is my large upgrade. I bought a 6' 180 a few months ago, but sold it because I simply don't have the room for it. That's why I went with the biggest I could fit in the space I have. I'm going to be plumbing this tank through the floor into the basement so I don't plan to move it.
I just got off the phone with EcoTechMarine's tech support. They said 10mm is slightly too thick for the MP10. So I'm going to start off with one MP40 and go from there.
Not sure on the return pump yet. I'm still researching them. I'll have about 10 feet of head so I'll need a strong pump to get some good flow out of it. Hmmm...my next thread topic has just been born.