It looks to me like the majority of the work contribution to Seventeen or bust is now coming from the PrimeGrid project. While sieve has been dominated by primegrid for the past couple of years now PRP testing through primegrid has overtaken users of both the old client and new prime95 client.

I'm basing this judgement on the stats pages found here:

http://www.seventeenorbust.com/stats/ and here:

http://primegrid.com/stats_sob_llr.php

Which show that the number of pending tests on the traditional clients is 1951 vs 2126 in progress at primegrid.