Have owned and enjoyed sk2 (for about 3 years), playing ensemble work at church with occasional bass work as needed. Agree with Jim about bass, adding that IMHO the vent appears to emulate low bass roll-off of 122/147 a little too well. (Played BCV-Trek3 console for years many years ago in trio environment so I know bass limits of old large Leslie very well). Ensemble-wise there is no competition to my ear - definite advantage to vent, particularly noticeable on fast speed. Just received XK5 in mid January, so more time needed for fair assessment. Initial impression for XK5 is same as SK2, however. And I still haul vent to and from church engagements, so I am "walking the walk" so far with respect to my opinion of vent on XK5. My plan was to sell vent to offset cost of SK5, but not willing yet.
BTW I conducted short side-by-side comparisons, using bypass functions on NEO Vent and on both instruments. I hope this helps.
Also, while posting, playing XK5 takes me back to "old days," only with more adjustments available. Love it!