My E9 puts out around 317mW into 150Ω and they sound fantastic, so you shouldn't have any problem.
I think $730 is fantastic deal. Sennheiser should price them: HD650 for $350, HD700 for $700, and HD800 for $1400. I think they would sell more HD700's at that price, they wouldn't be so close to the HD800 then.
Edit: I also feel the LCD-2 should be around $600 not $1000
Agreed. The 700s run a bit cheaper in Japan by about US$100, but some other phones run much higher, but some more cost separation from the 800s would probably help sales and probably dampen some of the negativity. They are great phones though, am rediscovering a lot of music through them.