What do you mean slower?
edit: I went and took a look at the rieselsieve page. It's gonna be slower cause the linux portion has to use prothsieve rather than jjsieve which is very noticably faster on rieselsieve. So while I wish to offer congrats to AMDave and Bryan on their achievement, I don't plan on participating in the boinc rieselsieving until there is a jjsieve for linux with the same rough speed equivalency.
There is the same basic issue with psp sieving too, however the speed increase for windows using jjsieve isn't as great for psp sieve as it is with rieselsieve. But at some point here I'll be backing off psp sieve too. My electric bill is eating me alive.