Try a smaller pool for low hash rate, that way you will get a larger payment when the pool hits a block.  I have several usb miners ~55GH/s at https://bitminter.com/.  It is PPLNS but the pool is only ~3PH so your low hash will still earn payments each block.  You can also try http://www.bravo-mining.com/index.php and http://www.bcmonster.com/, both really cool small pools, they are PPLNS but each shift runs for as long as it takes to solve the block so you get paid for every share submitted right now and they usually have good promos.