Had the bespectacled young lass who graces the beginning of this lively thread been employed by Gibson in the late eighties to promote the IV/V (for the 5 string model) line, history might have been different ...
Alas!, 'twas not to be: In the words of its creator, Phil Jones (then junior luthier at Gibson and not to be mistaken with the amp designer), the IV/V was "Gibson's failed attempt to bring the TBird into the eighties after the failure of 'The Loser' " (less than respectful internal Gibson moniker for the Victory model which sold like lead by the mideighties). The TBird was a classic shape, but unergonomic to many bassists with bad upper register access, break-prone at the fragile neck-huge headstock transition zone and expensive to make due to the neck-thru construction. So Herr Jones, who despised the Victory as a "bad Fender knock-off, Gibson never got bolt-ons right", set about creating something modern, yet Gibsonesque, a return to mahogany tradition (as opposed to the many maple models Gibson had released since the late seventies up to the mid-eighties), set neck, ergonomic with added frets and affordable too. He thought. He didn't get much farther than headstock (a nod to Gibson tradition in the Grabber and Flying V vein and also stylishly "eighties") and mahogany, when the sales department intervened and demanded a shape which reminded of a Victory body drawn by a child (Jones was a fan of the LP Junior shape). Adding insult to injury, Henry J, then already Gibson CEO, demanded a 1.000 buck price tag to the bass which killed it commercially. It bombed, didn't last long and the end of 1987 saw the reissue of the real TBird in pretty much its classic shape (which made the concept of the IV/V redundant), albeit with a smaller headstock for better stability and balance. Both models incidentally used the same pups.
If you can get over the ugly "Fender larvae" body (I thought the less rounded Victory shape cool, but the IV/V shape is just anodyne and reeks of Fareast budget bass of the worst kind), the IV/V leaves you with a very ergonomic and comfortable playing experience, approximates a TBird sound (a TBird offers more sustain due to the neck thru construction, but the IV/V is no slouch in that department either as you will have undoubtedly noticed by now, also the pups used by the original IV/Vs and reissue TBirds called TB Plus pups have been consistently souped up over the years for more output, older ones have a tendency to be microphonic) and gives you a high E whereas a conventional Bird already has you struggling with a high C#!
While my IV did indeed have a price tag, it was second hand and bought in this millenium, factory set-ups had long vanished. From my experience (I have one IV and two five string Vs which have a slightly thicker and wider neck), IV/Vs can be set up with lower action than a TBird. The cavity for the truss rod nut tends to be a bit tight for full adjustment tool access, you might have to make a little room via scraping away some of the soft mahogany behind the adjustment nut with a screwdriver. The neck can be very straight with little relief.
Our freelance contributor and TBird collector, the honorable George Carlston, once described the IV/V as "a TBird, albeit in Clark Kent mode". That sums it up nicely.
Uwe (currently on business in England and now late for dinner due to your collective call to arms!)