As Brent would say, here is my .02 worth. Generally at FL 290 you are above the clear icing level. A good rule of thumb is that when you reach -40 Celsius you will have no hassles with ice. Around -43 celsius is standard at this level. I have flown my IV to FL 290 quite often to avoid icing. The true airspeed was well above 300 kts but the downside was that the cylinder head temperatures sat aroun 410 F. I put this down to the turbo's working so hard. The airframe (with winglets) was still very positive to hand fly.The mountain high system was not giving an adequate supply at this level, so we were constantly using the button to give continuous flow. Your main consideration going to FL 290 is the climb & descent (with regards icing) & if there is no possibility of embedded thunderstorms in the cloud. Remember also that your temperature gauge has ram affected errors that need to be corrected. Regards Gary Burns.