On a 100hp Rotax 74lb = 3hours (about 70% power)
You are quite right about the useful load of a micro. I would only go for a 3 axis micro if I had a licence restriction or a planning restriction on my home base. In all other cases you go VLA, which has the same running costs but much more useful load (in some cases it would be an identical aircraft but different paperwork)
If you take a SportCruiser VLA for example;
You could get yourself, your identical twin, 4 hours of fuel and some bags! And travel at 100kn
A VLA homebuilt can also have
a (certified) Attitude Indicator
de-icing of the pitot
a secondary static source
certified navigation instruments allowing positional awareness out of sight of the surface.
I have to say that my MCR has non of the above, but the uncertified kit I have fitted is vastly superior to any certified kit unless you are talking £30k plus just for the EFIS. It is however capable of short bursts of IMC in the unfortunate event that I get caught out by the weather.
Rod1