I just reviewed cycling peaks for the season. Every 20 minute power is about 30 watts higher on the TT bike. I simply don't do sustained Threshold or above threshold blasts on the road bike (Though when I get to do longer climbs in France, maybe) unless I am in a paceline. My norm 20 minute power on the road bike has been around 390 for twenty minutes with my norm TT bike power at 383 in the same week. The average road bike power was much less though.