Hi there,
This design might be a bit of a stretch, therefore most likely you are going to need the best components available.
With boost converters with very high output/input voltage ratios there are limits as to what the switch resistance and input resistance combined with inductor series resistance can be. The reason being that if the combination of these is too high then the needed output voltage can not be realized. The reason for that is because the gain with duty cycle actually goes down instead of up after you reach a certain point. That means that you may not be able to get the full output voltage (24v) with low line (6v input) just because one or more of these resistances is too high.
Luckily, we can calculate the maximum value that the duty cycle D can take on for these given resistances and a good approximation is this:
Dmax=1-sqrt((Lesr+Ron+Rin)/Ro)
where
Lesr is the ESR of the inductor, and
Ron is the 'on' resistance of the switch, and
Rin is the resistance of the source (in series with the input), and
Ro is the output resistance, and
the voltage drop of the output diode is assumed in series with the output voltage.
If the value of D goes above Dmax for any input voltage (low line is worst case) the gain will actually go down meaning the output voltage will decrease instead of increase as it always does up to that point.
This relatively simple equation allows you to calculate what your inductor resistance and switch resistance need to be in order to get the output you need. Because this design is so critical, i have to wonder if you have tested it at low line yet.
One way to get a better overall converter is to parallel two mosfets. That reduces the switch 'on' resistance of course. You do have to observe proper techniques though when doing this.
As a quick example, with 0.05 ohms switch 'on' resistance and 0.05 ohms Lesr and 0.05 ohms input resistance and 6 ohms output load you will not be able to obtain the full output of 24v with only 6v input because the duty cycle required for that would exceed the calculation of Dmax above.
You can estimate efficiency by calculating the power losses in each component taking into consideration the current flow and the 'on' duty cycle of each component.
And yes, the current waveform through the MOSFET should be out of phase with the voltage across it, but make sure you have all the test equipment hooked up right.
BTW, have you mentioned the converter switching frequency yet? You might want to look at the effects of higher frequencies in the inductor using 8 gauge wire which may not be the best choice at all due to skin effects. You do have a relatively high inductance value so that should help though. You might also want to estimate core loss in the inductor.