Rainbow Bridge - I never said he'd WANT to use it... 
Ring capacity - Sinestro has worked with GL when there are greater threats out there - but yeah, it tends to be the End of the Universe grade threats that are the ones that get them to work together (DC's Brightest Day/Blackest Night was the most recent one they were forced to work together in).
RMH
If we knew what it was we were doing, it would not be called research, would it?
- Albert Einstein
Ring capacity - Sinestro has worked with GL when there are greater threats out there - but yeah, it tends to be the End of the Universe grade threats that are the ones that get them to work together (DC's Brightest Day/Blackest Night was the most recent one they were forced to work together in).
RMH
If we knew what it was we were doing, it would not be called research, would it?
- Albert Einstein