> What's the fastest T1?

The only one announced so far:

https://morph.zone/modules/newbb_plus/viewtopic.php?forum=3&topic_id=7001&start=736

> What core is to used in T2-T4?

"e6500 core running up to 2.5 GHz (T2-T5 families)"
http://www.freescale.com/webapp/sps/site/overview.jsp?code=QORIQ_AMP_SERIES