Packet drops on the interface statistics

Most stats don't

However the numbers themselves are a counter. So what I'd normally do is to poll the counters and save them somewhere... An RRD, or something more sophisticated. Then graph the difference between successive readings and it becomes obvious when the drops occurred.

Cacti has a fairly good set of stats for both specific BigIP counters (LTM/GTM/APM etc) and generic network level stats which will include your drops as well. But you could use nags or solar winds or whatever you prefer.