I would say as slow as you can safely and not hinder traffic or drive you insane. I don't know about the 06, but with the instant guage, when feasable, I try to accelerate with assist at the highest possible mpg ... which is one bar shy of 40 mpg. I have found not a huge difference with accelerating between 20-30 mpg, but higher is always better, just think of h.s. and doing averages. If you accelerate at 20 mpg for 20 seconds, you will have to drive at 80 mpg for 20 seconds to maintain 50 mpg average. If it is 36 mpg, the you would only need 64 mpg on the glide side. I was trying to teach myself last night, but unfortunately it was 40 degrees outside, I didn't realize that until I got home. I could only sustain my speed/glide at around 60 mpg except for a few sections, but the few nights previously when it was around 70, I was able to keep it around 80 much easier. I still managed to raise my mpg from 52.6 to 53.3 with the hills, traffic, and coldness, I have about 320 miles on the tank. I don't know if it is a quirk of the HCH I, but I can get better mileage in the city with my personal technique. I drove mostly at between 45-55 mph, some of my pulse and glides took me to 60/65 and down to 40. I am planning to do this trip again when it is warmer. Oh, I also had my first forced regen, but it was at half charge, I thought it would be lower than that, but it still maintained 60 mpg.

So to put it simply, accelerating at 1500-2000 would be best, especially if you have lights and you utilize coast and regen. If you will be able to hold a high mpg for a long time, you can accelerate quicker if it pleases you and still achieve great mileage. But always put safety first, and drive how it will make you happy, it is your new car, no matter what you do, you get better mileage than 99% of the people driving similar.

I will pass the advice that xcel told me.
just switch HCH I for HCH II ... I am sure he would have the same thing to say to you ... and remember, you still have break-in time ... many have said the FE goes up several times in the first 10k and I think I read it will a few more times up to 30k miles.

If you can find out any new information on you tests please share! You may find something out that no one else has before

Take care and have fun!!!