"Mike Granby" wrote in message
oups.com...
So I'm flying IFR down V441 in Florida today, when I hear the
controller who's working me call traffic to a VFR airplane he's
providing with advisories. "Traffic, twelve o'clock, opposite
direction, very fast, same altitude, suggest you descend now." The 172
he's talking to descends in a hurry, and the traffic passes without
being seen. A few minute later, the controller says the same traffic
has circled around and is now coming back at the VFR airplane once
again. Once again, negative contact. Next time, the traffic is reported
circling ahead of the 172, until he breaks off and again makes a pass
around the Cessna. This time the now rather panicked VFR pilot see the
traffic, and reports it to the controller as "some sort of single." The
controller points out that at 250 kts at 5000 ft, it's unlikely to be a
piston and it must be some sort of jet.

I wonder if it was one of these?

http://www.if1airracing.com/IF1_Planes.shtml

These guys tend to fly around in circles at 250kts.