I changed conf to this
addnode=explorer.biblepay.org
gen=1
genproclimit=20
minersleep=0
tithe=10
nickname=pagalo
tithing=10
CPU load still about 10%. It varies from 5.5% to 13%
Ok, on a side note, Im at 50% load on my windows box with genproclimit=20 (as a test), but let me look at the minersleep code, hang on.