The same geometric network using esri's data type works fine, and is really quick. I'm not expecting geometry to be as fast as esri's, but it should be closer than what I'm experiencing. Statistics and indexes on sql server 2008 are good to go--if I could just use something other than ESRI ArcStuff, I wouldn't be posting!
It is an ESRI issue with an open incident. But frustrating nonetheless. I'm still working through it--I'll post updates.