Seems like its going to be a tight race on breaking even with new ASICs like Cointerra coming onboard. Timing is now critical. If you guys get the units end of Oct, and overclock the HashFast units to 500GH then IceDrill will more likely make a ROI.
The HashFast units are easily overclockable (To probably 550-600GH I imagine with the correct cooling)
The latest publically shareable information from Hashfast on the topic of overclocking can be found here:
Metal migration is a well understood phenomenon. We have followed all the fab's rulesets for electromigration so that the current levels we're going to see will not be a problem (even current distribution, and thicker metal layers). Currently in the simulator for EM our chip passes the test for a 5 year lifetime, but fails the 11 year test - and that is running somewhat overclocked, at about 540GH/s.