You can usually (but no always!) convert a 2 pin electret to 3 pin with a slight modification - called the "Linkwitz mod" but I'm sure others have done it before. NiHaoMikes link provides all the details.
I've found the 3 pin ones to have lower sensitivity, but also more linear. As for noise, theres a great deal of variation, as there are so many cheap electret capsules, even some of the cheapest can be remarkably good.