Selecting AVR microcontroller with or without PicoPower?

I have been using ATTiny13 DIP AVR's for a few years, for very simple projects. I'm now expanding and switching to surface mount devices.

I'm a little confused about some of Atmel's offerings; let's take one example, the ATTINY26.

Specifically there are so many variants of this that I have no idea what to select. If I select non-reel SOIC, I'm left with three choices:

• ATTINY261-20SU: 20MHz, 2.7-5.5V


• ATTINY261V-10SU: 10MHz, 1.8-5.5V


• ATTINY261A-SU: 20MHz, 1.8-5.5V (PicoPower)

Based on these, is there any reason I would not want to select the newer "PicoPower" (1.8V) capable AVR? I realize that the clock speed decreases with less power. In my application, I do not need to take advantage of the lower power operation. Since the cost for small quantities is similar, there's no real advantage that I can see to selecting the slower 10MHz version.

Bottom line, is there any reason to opt for the older and/or slower (first two listed) rather than the newer low-power version?

Edit:

PicoPower on this device is 1.8V, not 0.7V. (I must have misread part of the datasheet.)

Answer

PicoPower AVRs are not necessarily slower. If you want them to run on low voltage, only then you have to run them slower.

Older "V" devices tend to be inferior in sense of speed, newer PicoPower as far as my experience goes (I'm building my first low power design now) can run as fast as "normal" devices when powered from 5V.