Isn't the shop going to get a ML '57 in shortly? If so, I think I'd play that first, then decide if you can live with the aging or want to find a VOS '57. If you decide the VOS '57 is a better fit, I know they are in stock at several dealers that will offer you a deal. From everything I've seen lately, Gibson's quality is good enough that buying a specific guitar sight unseen isn't nearly the risk it used to be.
As for the '50s Standard vs '60s Standard, Gibson lists the '50s as having Burstbuckers (Alnico 2, 8k) and the '60s as having '60s Burstbuckers (Alnico 5, 8K). The Reissues (both the ML and VOS versions) use Custombuckers (Alnico 3, 8k).
My opinions on these three pickups:
- The Custombuckers ('57 RI) are really nice, warm, bright, and not very compressed at all. These are my favorite of the bunch and hold their own against anything I have right now (Throbaks are on the way, so that may change).
- The Burstbuckers ('50s Std) are good, too, a little more modern sounding, but nicely compressed. These are really nice pickups and, without having compared these directly with the other two, I'd say they were great (but I did compare them and they're still good, just not my favorite of the three).
- The '60s Burstbuckers ('60s Std) are a kinda between the two, not as modern sounding as the BB but not as vintage as the CB. They're brighter and the bass is stronger, but not overbearingly so. They're still warm and decently compressed (easy to play). From what I have, they're most like the BKP Riff Raffs, which is a later PAF/Patent-Number/Pre-T-Top type and were a good fit in the '61 SG that I played them in. Based on what you've said about the sound you're after, I think these may be a better fit than the Burstbuckers in the '50s Standard and close (but not quite) as good as the Custombuckers.
- It would not surprise me if the only difference between the BBs and the '60s BBs is the magnet. I haven't measured the individual coils, so they may have different offsets, but they're both right around 8k, unpotted, and what I'm guessing is 42 AWG Plain Enamel. The differences I hear aren't too far off what I've experienced changing magnets in other pickups. I think the Alnico 5 of the '60s BBs just works better in that pickup, at least for me, and I could be wrong about how closely related they are. I'm curious if the Alnico 5 is a short magnet, degaussed, unoriented, or what, because they do not have the sharp highs that a lot of Alnico 5 pickups seem to have.
- I think that the Custombuckers ('57 RI) are a little more vocal. I think they're a little more microphonic (in a good way) and pick up a little more of the acoustic sound. To me, they sound like they have a little more scatter in the wind, but I have no idea if that's true. I'm really looking forward to trying these with the Alnico 4 and Alnico 2 magnets that are also on their way from Throbak. It would not surprise me if these are very similar (or the same) as their '59 Collector's Series pickups. Those sound really really good, but they're using Alnico 4 and sound like it where the Custombuckers use Alnico 3. I'll know more about this by the weekend, with any luck.
That said, and as I've said before, I think the '50s Standard was a great guitar and I have no doubt that the '60s Standard is, too, although I haven't played one recently. However, when I played one back-to-back with my '60 Reissue, it was obvious that they were not in the same league, just from how it felt in my hands and more than just the neck shape. To me, it was worth the price difference and now, I actually want another (someday). If I was looking for a gigging guitar, I'd get the '60s Standard and not worry about it getting damaged (or worse) because I prefer thinner necks and I think the stock pickups sound good enough for live work. If I was looking for "the one" and was willing to spend the money, I'd pick the '60 VOS all over again in a heartbeat because it really is that much better, to me, and I don't really care for pre-aged guitars. Although, I understand why some do and, if I was looking for a replica of a specific guitar, I'd be all over the Murphy Labs stuff.
BTW, I completely understand where you're coming from; it took me forever to decide on which one I wanted, probably asked more questions than you have, and spent the better part of two days playing about 20 of them. No matter what you decide, it should feel like the right decision for you. I haven't regretted my choice for a second and you shouldn't either. I guess what I'm saying is that I think you're taking the right approach and asking the right questions.
Edited for clarity.