I have the ST8130, and then bought the lap timer and beacon seperately (for a steal out of the 'states, but from memory you can get them for around $500US). If you've already got the Racelogic then maybe you should keep that as the data logging features for the Stack are ridiculously expensive.
As far as fuel is cincerned, yep, that's correct. We're havign dramas with mine calibrating at the moment, but my fuel float is buggered so I'd say that's the issue for me. Also getting the speed sensor to work has been a bit of an issue, but we haven;t spent too much time on it as we've had bigger issues to deal with!
When assessing which system to get I spoke with my mechanic/auto elec aqnd he felt the Stack was the easiest to set up due to the configuration of the loom. He didn't run into any dramas, and it was all pretty simple, and very neat.
As far as the Defi dash goes, I think it's the nicest dash out thee, but being Japanese only I was worried about some of the functionality, including the GPS based track timing, and in the end decided against it. Perfect mix of everything as far as a display only dash goes though imo.