Re: original 550 vs newer models and 20th annys
i've tried and worked on four Annis (2 BKs, 1 DY, 1 RFR) and countless older 550s (i also own quite a bit of those). all i really can tell is that the Annis are as sturdy as a tank, very well built and assembled (very stable neck/body joint). you just worry about playing with an Anni. the older 550s have a more "loosened" feel, and often they are, but hey, they sound as hell, especially those from early '90s (old-heel). you can barely feel tons of vibrations running down the neck and stepping onto your arm and belly. wow! the Annis i've tried didn't sound like that, they're probably too young, or it's because of the different neck construction (550s = 1-piece neck; Annis = 5-pieces neck). that's the most difference i've found.
so you got goodies from both, you just decide what's your cup of tea. of course they share common features: a very sleek and comfortable neck (Wizard) and fretboard, and a problem-free trem (Edge). great guitar, indeed.