I have the W3 and love it. I dove Blackbeards livaboard in the Bahamas Feb/Mar and was fine in just the W3 and a LavaCore hood. I find it sufficiently stretchy but I am toward the smaller end overall because my limiting size is shoulders/chest in most cuts. Lining is great but does take time more time to dry compared to my old Henderson GoldCore (smooth). I imagine the W5 may be a faster dryer at the expense maybe of some loss of warmth. I would look at the pockets and see if there is enough space in there to be a significant differentiator. I have 2 large utility pockets on my Batwaist-belt for warmer diving.
But it (and the W5) are only 3.5mm compared to the 2.5mm of the W30. Are you looking for a quantum step up in warmth? I would consider adding a vest (or hooded vest) first for maximum flexibility. I have a LavaCore vest for a quick bump.
Then step up to a 5mm W4 or W7 if you are looking for significantly more warmth.
ETA: Whoops. I was noodling around the waterproof site and failed to consider that you may have the shorty rather than a full W30. So a Full 3.5 should be a quantum step up from a 2.5 shorty.