The XW's get 5 degrees wider field and a much fatter price tag.
The XL's are discontinued and only available second hand.
65 degrees vs 70.
The 80 degree field of a nagler can give a feeling of sticking your head out into space, versus viewing through a large window with the pentaxes.
With a wider field you can go shorter on focal length and get a darker sky background, but the eye can only critically examine a field of 60-70 degrees at any one time with the rest being perepheral vision.
The pentax is definately sharper with less scattered light on planetary viewing even with a barlow. The 12mm nagt4 was absolutely horrible barlowed ! Pentax coatings are second to none and I reckon give sharper views than short focal length nag type 6's.
My 14 and 10.5mm pentaxs, coupled with my ultima barlow give me effectively four premium eyepieces and superior planetary views IMO.
Dave47tuc Im sure will have some valuable input here as he has looked through my pentaxes and has tried nearly every nagler known to man
Its a personal preference thing and id love to have both.
Naglers or Meade UWA for DSO's, but definately not dual purchase barlowed.
P.S. Anyone contemplating purchasing premium eyepieces should do it now while the Aussie dollar is in such a strong position.