I've used the Stalker v2 in several projects - it's a nice integrated solution if you need all of the features it provides (RTC, XBee socket, Lipo charge circuit, solar support, and sd card). Beats the heck out of an arduino and a stack of shields. The question is why are you looking for a 5V version? If you have a 5V sensor that you need to integrate with, just use a level shifter and a boost converter (pololu makes an extremely efficient 5v boost circuit that is quite reasonably priced). Or find a 3v replacement for the part - it's bound to be cheaper than a new microcontroller.