You can fly the Columbia rich of peak and burn 24 gallons to get an extra 10+ kts on top of that, but that is silly. 235-240kt TAS at FL240 is nice to prove a point, but hardly sensible.
It just hit me that the speed difference you are seeing is due to flying ROP on the Columbia. You are correct about the speed difference in that case. A TN22 is always flown LOP in cruise. In fact, the way you fly it is ROP and WOT in the climb and then 2500 RPM and 17GPH for cruise i.e. no lean assist or setting of EGT's. If it isn't hot then you can do a LOP climb on the Cirrus.