Gent's thanks for the info! I'm doing a QuickFIX interface to Nexa and, after meeting Chaz & Partick @ the Trader's Expo in Chicago, plan to integrate RedSky in the near future.
I haven't done a full load test to measure performance but it appears to be as fast as the X-Trader platform for both market data and fills. As to standards compliance, I'm sure you're aware that anyone who has this API had to sign a NDA so I can't comment on specifics. There are custom fields and messages and you can consider those non-standard but that's just life: I don't expect a FIX 4.2 API to be re-written when they just want to add some FIX 4.3 messages. The API works well and the TT folks are very responsive. Hope it helps, Francis