Sounds like a pretty high number to me, but may be possible.
I didn't run across any 56TC numbers on a quick search but I'm sure that they are out there.
The think that the Baron 56TC uses the same 380 hp engines as the Duke, and a quick check shows the Duke rated at something like 233 knots (way up high, I'm sure). The Baron with 310 hp engines is rated at 75% power at something like 213 knots, so the 56TC may run up into the mid-200 knot range at oxygen+ altitudes.
Someone doing a little more homework could probably give you a more exact answer...