Thanks all for the responses.
Quote:
Originally Posted by KEP
According to that page, wich holds records of TF bitdepth for all n>1000M to n<=2^32, the optimal bit level for TF for n=3321930371 is 91 bit.

Interestingly, according to the following link, factoring to 91 bits would require over 150K GHzdays of computation, while a LL test requires only 91K:
http://www.mersenne.ca/exponent/3321930371
Perhaps I'm misreading it, but that seems to imply that 91 would be too high, or one of the estimates is off, perhaps due to it being so far outside of normal assigned ranges.