Let me share some of my findings on VSD5, been lurking here for a while. Brief background of me, my I had a few vsonic iems in the past, started with GR02 Bass, GR07 Mk2, VSD1S. So yesterday I to drop by at the store(actually is a locker) had a chance to get my ears on VSD3, VSD3S & VSD5.
On VSD3, the bass is punchy & dominating, music is aggressive(fast decay) and drums is better here too, treble is smooth with a hint of sibilance, can't comment much on the mids as I noticed more on the lows and highs.
On the VSD3S, the sound is akin to VSD1S, not as aggressive, sounds more mellow, the mids are more pronounced, bass is still present and punchy yet not dominating, up on the highs, the treble is business as usual, but sounds more peaky and sibilance is more here that reminds me of VSD1S. Both iems have a 'fun' type of detail which is what vsonic is known for its midrange iems.
On the other hand, VSD5, while still retaining the 'fun' sound of VSD3/S, has a better detail & layering, improved bass, which is deep, solid & doesnt drag too, vocals are more pronounced and has a good body, highs are are smoother & the good thing is the sibilance is substantially lesser than VSD3/S. Speed wise, just a tad faster or the same VSD3S. Ultimately, I'm leaning towards VSD5 because mainly of the treble, detail & the layering'and the vocal quality which is substantial improvement from VSD3/S.
Hope my findings help you to decide on VSD5 because myself just got one too...