That's the thing. Normally Intel controllers have bad write speeds with the smaller sizes. This one manages to get decent write speeds with very few chips. Heck, I just looked up published sequential writes for Intel drives:
X25-V 40GB 35MB/s
X25-M 80GB 70MB/s
X25-M 120GB 100MB/s
X25-M 160GB 100MB/s
320 40GB 45MB/s
320 80GB 90MB/s
320 120GB 130MB/s
320 160GB 165MB/s
320 300GB 205MB/s
320 600GB 220MB/s
311 20GB SLC ~115MB/s
So, older G2 can't match the write speeds no matter what. For G3/320 (LOL "G3" is in the part number in place of "G2") this 20GB has write speeds between the 80GB and 120GB. The normal selling prices of those drives are $190 and $240 (currently discounted to $185 and $220). Thus, the 311 gets better write performance for less money.