With Stratum, your efficiency is always going to be extremely high if you're mining on basically any GPU/FPGA.  Basically 1 share [diff1] per 30 seconds = 100% efficiency [if I'm remembering correctly], and it scales from there (1 per 15 = 200%, 1 per 10 = 300%).  I may be wrong, I can't remember exactly how efficiency was calculated on Stratum, since you basically receive 1 work unit per 30 seconds regardless of your speed.  The stat is mostly useless because of that fact.