I've got a Classic Prius so my A/C is belt driven by the ICE vs. the electric AC of the HSD Prius, so YMMV, but I find that once you have the cabin cooled to a decent level, switching to recirc and floor level vents, results in a nice comfortable cabin, with the A/C compressor running relatively infrequently. At this point, if you also turn *up* the temperature dial a click or two, the compressor runs even less and there's no real difference in cabin comfort. Aside from the initial hit when the A/C has to cool down a hot car, when I run floor level recirc with the temperature up two clicks with my A/C, there's not a lot of difference in MPG: once the condenser is cool enough, the A/C will stay "off" and I can still do extended runs of stealth at 98F, and the ICE will stay off through most stop lights.
On the other hand, if I keep the bi-level going, the compressor runs a lot more often- I can't sit through more than about 5-10 seconds with ICE off at a stop light, and my MPG gets a very noticable 3-4 MPG hit (again, this is on a Classic Prius with belt driven compressor). According to the NCF booklet, the A/C ECU seems to use the climate control settings on the console mostly as a suggestion and the computer tries to figure out the best settings, so on bi-level it tries to use more outside air (even if recirc is on).. The outside air is usually hotter than the internal recirculated air, and the bi-level also tends to move more air volume around, which means there's more heat exchange needed at the condenser, and thus the compressor has to run much more often to keep the system cool...
