Any reason to not just go all out and use the H110?
"going all out" is relative. Instead of using some closed loop system, why not make your own? I honestly think a 2x120mm radiator (let alone 1x120mm) is far too small for such a huge load such as the hashfast chip (600W or more). The included fans likely don't have very good air pressure either.
The fans are actually a bigger issue than the radiator, to be honest. Most aren't designed to push a lot of air through a constricted spaced. While I was down there we were able to run one of the production Habaneros up to 925MHz with a non-ideal clamping and no backplate (they hadn't come in yet) using an H80i, but it had a high flow 38mm San Ace fan on it. It performs much better like that than a double radiator like the Swiftech H220, Antec Kuhler H20 or Coolermaster Nepton 280L with stock fans.