I've always thought the best mpg when accelerating up a hill was achieved by keeping the engine at or just below the "max torque" rpm of the engines torque curve. The rpm that the engine produces the most torque is also it's most efficient rpm under (a heavy) load. (I'm not convinced this holds under light loads with modern engines using VVT, lean burn, or cylinder deactivation)

The '07 HCH rating is 123 ft-lbs @ 1000-2500 rpm. It would follow that keeping the rpm's at 2500 rpm would give the best acceleration with the best mpg. Obviously if the hill is too steep to accelerate to the desired speed at 2500 rpm, like teiresias experiences, then a higher rpm is needed. The HCH reviews comment that the engine features a broad and flat torque curve. So the engine's efficiency would not suffer much at 3500 rpm if needed. In my humble opinion, I think accelerating at a reasonable rate and then backing off the rpms to hold the speed usually will result in a better overall mpg than slowly accelerating up the entire hill.

 

... with snips ...
At least on paper, that seems to make sense. However, having tried both the snail and the jackrabbit, I can say without any doubt that the snail is more efficient. Why, I dunno. It just is.

 

Let me preface this by saying my commute is a third in the city and two thirds rural highway (2 lane).

It depends on how far away the next stop light is. For me if it is less than a mile I try to keep it under 1500 RPMs. If I'm going down hill, I try to coast as much as possible to get the 100 MPG for as long as possible. If I'm going up an incline I'll bump that to the 2000+ range and use the assist.

If the distance is greater than a mile between lights or it is my last light before I get to the highway, I'll try not to go over 2000 RPM. When the FCD shows my MPG getting below 40 then I lighten up on the acceleration until it gets back to 45MPG or better. Overall I increase in speed about 1 mph per second and yes, the NASCAR wannabe's pass me like I'm standing still, but I'm getting 65 MPG. So they can bite me.

Of course the top speed for me is usually 60 (if I have the road all to myself), but I keep it around 53 to 55. I've found that even if I'm doing 65, there's always a fool with a MPM (Must Pass Mentality) behind me that thinks I'm driving too slow no matter what speed I'm driving. So why waste the gas and try to make them happy when they'll pass me anyway?

It works for me and the car nearly has me trained.

Good Luck and keep practicing you'll find your middle ground.