Quote:
Originally Posted by Batalov
Here are the fairly good rules of thumb:
 for SNFS, with every 9 additional digits of SNFS difficulty, the overall runtime will double (or, which is the same, runtime will be 10x for every 30 digits)
 for GNFS, with every 5 additional digits of length(N), the overall runtime will double
Remember just these two and you will be in good shape.

Interesting, thanks. I suppose these will actually overestimate the time for large enough numbers since the complexity of NFS is subexponential, but if it's a good approximation then that's fine.
I did a C165 SNFS in ~5h30m yesterday and the one I'm currently doing is a C201, so ~16 times longer = about 3 days 16 hours. That's quite a lot less than I was expecting actually.