Thanks for the tip about them being the same chips as the S1! I think I saw a 225 S1 setting somewhere so I'll try the magic hex from that to see if I can get her rocking at 225 ... will report back! 
Yeah, 225/6386 thus far (30 minutes in) is giving me about the same hashrate (0.85% increase), and more than double the hardware errors (7.43% vs. 2.33%) ...
The only hex I could find for the frequency in the middle (221.88), 6306, doesn't take on the S2, so I guess I'm sticking with 218.75 until they release their official upgrade path ...