So do you reckon if my average speed on a solo ride was about 19mph for a 1 hour 30 min ride I could stay in a race bunch?
Potentially, but it's not quite as simple as that. Road/circuit racing is not really about maintaining a steady average - you need to be able to cope with the surges and attacks that typify most races like that. You need a good level of fitness (which usually manifests itself as a decent average speed over a training ride), but you also need to be able to ride at, or beyond your threshold for short (and sometimes not so short) periods of time.
I've been in races with guys who I know can ride faster and climb faster than me at steady state efforts - but they've been blown out the back of a circuit race within the first two laps, because they couldn't cope with the changes in pace.