There will be a significant speed increase, though it will be a bit lower than 9%, as effort seems not to linearly scale with the amount of k's: Riesel has to sieve for 8 times as many k's (and uses even a slightly bigger range), but one only gets a slowdown to 1/5.
Beneath the amount of k's, the n range has an influence on sieving speed. I think it was ~ sqrt(n range), thus quadrupling the sieving range halves sieving speed. Again, it is even a bit less to my experience.
The amount of k/n pairs in the dat file is said to be unimportant when it comes to sieving speed, although some ppl claim a performance increase of 1-2% with newer dat files which have been cleaned from already found factors.
Concerning memory vs. performance considerations, mklasson is the man. But I doubt there is a way to feasibly sacrifice some memory for more performance...