As for FTL velocities, the speed limit is the same for antimatter as for matter. In relativity, it is causality, (among other things) that sets the speed limit of 'C'.

In general relativity it is the _energy_ density that matters... However, now that anti hydrogen has been made, several groups hope to do tests of antimatter's reaction to gravity, and spectroscopic tests to see if it really is identical to normal hydrogen. There are many papers on this by Dr. Gabrielse- the leader on the experimental side of this field.

If the reaction of anti-matter to gravity is different, then it is a violation of Einstein's Weak Equivalence Principle (WEP). While not expressly forbidden, (I think), such a violation would come as a big shock to physicists.

I think the majority of scientists agree that if you found an asteroid made of antimatter, it would be indestinguishable from normal matter until you dropped something on it... preferably from a distance!