I can see the logic of all the logaritms, but i prefer a faster way to calculate efficiency :
Right now i'm popping out a factor a day or so when sieving, and a full PRP-test takes about a month or more. (running 4core, so should correct for that... let's say a week) That means that sieving is about 7 times as efficient as is, so i'll continue sieving :P

@vjs : just a bit more than 1% of total resources... and probably not worth the effort... But hey, we're not even close yet Once sieving reaches 50T we reevaluate, can always switch, but it'd be much better if the PRP-ers switch to us first