I dont own MS1 but i do own MS2, and i can only assume it's worse than MS1 because i assume it's heavier due to larger, metal cups.
I find that grados aren't uncomfortable, but they're not comfortable either. For a bit of a metaphor for comparison, grados are not like sitting on a nice leather couch, but they're not like sitting on an old school plastic chair either. Grados are like a nice respectable office chair: i could sit on it for hours without complaint, but i wouldn't fall asleep on it like a nice leather chair (although, for the record, i have actually fallen asleep once or twice wearing my MS2s... while sitting on a nice leather couch
They may be uncomfortable at first, so many people dismiss them after experiencing this, but after bending t he headband and wearing them for a while they get MUCH better. I didn't actually bend the headband of mine- i let it bend naturally over time due to being on my head and being stretched when i put it on and off.
As for heat, i wear them outside in australian summer without any real complaints. They sit on your ears rather than encompasing them, so it's probably not as bad as over ear phones