I haven't done an A/B in quite a while, but as I recall...
They're rather different animals...even though they're identifiably from the same family. The 5 is a very tall line source, so it's much more dramatic on the imaging front. IIRC, It's also much more dynamic sounding, no small trick since the 3.5 is pretty dynamic in it's own right. Obviously, the 5 is also visually rather striking next to the 3.5.
Tonally, OTOH, it barks up much the same tree as the 3.5. Bass extension and octave to octave balance felt similar. The character of the mid and treble was also of the same cloth. I'd suspect that most people who like the 3.5 will love the 5...tho that's just a guess.
If you have sufficient budget, and really like the 3.5 (albeit with some reservations), and you have the opportunity to audition the 5, I'd absolutely suggest that you do so.
Hope that helps.
Marty