Geoff, the XF is very much like the 10 and 7mm XW ito optical performance, but with a 60 degree FOV. The most obvious difference you will see between the XF and the Burgess is the FOV. Burgess feels a bit cramped on DSOs by comparison. The XF is wider by I'm guessing about 3-4 degrees.
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I recall seeing Mike Hosea over on CN saying that these work great at f6, but off axis sharpness is degraded at f5.
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I might have another look at it in the f/5 then.
Mike, HDs are on par with XWs for on-axis performance IMO. I think the Burgess is just a tad behind these two. But the short eye relief and pinhole lens would be the deal breaker for me with a 5mm ortho. The Burgess fixes all that. I think the comfort level of the Burgess would mean you'd see more with that EP. All the planetaries are $US99. I'd try ordering it directly from Burgess Optical.
Pegster, for a 6mm EP to be appear brighter than a 7mm you'd need severe deficiencies, e.g., < 74% transmission in the 7mm, and that is assuming 100% transmission in the 6mm.
btw. I corrected my comments about magnification being little higher than the XW (i.e. FL shorter). I thought about it and the diffs can all be explained by the smaller than advertised FOV.