Can someone educate me on the difference between the L500 and a Bill and Becky?
Bill and Becky is just what people call the genuine pickup. There is a lot of confusion about the naming. Bill Lawrence is the main guy behind the design, and his wife (who does most of the work on the site and phones) is named Becky. Their actual site is here http://wildepickups.com/
The L500 or L500XL is what both companies, Bill Lawrence USA and Wilde USA, call their pickups. For whatever reason, the Bill and Becky models tend to sound better to most people. They're both in the same ball park (both companies) though. Bill Lawrence USA was founded by an ex partner of Bill Lawrence, and there has been plenty of drama about who owned the name, etc.. Wilde USA is the genuine company.
There's confusion about what models certain artists use as well. Originally there was a pickup called the L500 that was popular with some artists. Then another artist asked for the same pickup to be made with less output. So the existing higher output model was renamed the L500XL and the *new* lower output model was given the designation L500. So at one point the L500XL *was* the L500, but now the L500 is its own pickup and the L500XL is the older version. You may hear/read people say "well so and so actually used this or that model, not this.." this is where most of that confusion lies.
Also, leading to some confusion is that certain guitars from Washburn have shipped with both the Bill Lawrence USA and Wilde USA models installed, since I mentioned they're close tonally and look more or less the same. The Bill & Becky (Wilde USA) people have had trouble keeping up with demand at times so manufacturers and artists have used the other source. They're a very small operation. If you phone them you will likely get Becky directly.