I think your size calcs may be off a bit, too. I pre-calculated the RMD160 values for all ASCII 1 to 5 character words, and the output is about 0.9TB in size. To increase to 6 characters would result in a file size about 95 times that (about 80TB) and to go up to 7 characters would result in an output of over 7000TB. And consider the amount of time needed to check 135 trillion entries.
How long did it take you to generate a rainbow table of this size? I'm just curious about the timescale (so hardware specs for reference would also be nice).
Sorry in case you already mentioned it upthread and I overlooked it.
That's one of the interesting things about SHA256 brainwallets (so long as you're doing this for fun) : it can be easy to find them, but it's also very, very hard. 
Stealing brainwallets is probably still profitable though, as I assume that the running costs are close to nil once you've set up the infrastructure.