So I spoke with someone at the Glock Store in San Diego (http://glockstore.com/
) yesterday. (Never had contact with them before, but so far, I'm very impressed with them. Everyone I talked to was very knowledgeable and willing to help. They found me an employee who personally owns a G39, who called me back promptly.
Matt says he absolutely loves his G39. In his opinion, it feels nicer to shoot than the G27. He said it's more of a "push" rather than a "snap", and he thought that if I was comfortable with the G27 (which I've tried), I will love the G39. He didn't think that getting ammo would become a problem, but he conceded that Glock does not tell (not even the dealers) who well the .45 GAP is really selling and what Glock's future plans are.
On the Generation 4 question, I was told (by another employee): Very doubtful that the more rare Glock models will ever make it to California in Gen4 any time soon. Maybe never.
They expect Glock to offer the rare models in Generation 3 for a long time. Glock has not even started the testing and approval process yet, which California now requires for each handgun model sold here. (It's one of these laws designed to make it harder and more expensive for firearms makers to sell in California. California requires a battery of "safety tests", and of course a fee, for each make and model. But these safety tests are almost a joke compared to what a manufacturer like Glock, or a law enforcement or military agency, does to the guns). So it only makes sense for a manufacturer to go through the approval process if they hope to sell a certain number of guns, otherwise, it is unprofitable.
But just as I had suspected: the G39 is not in stock, a bit difficult to find and they don't sell many, so it would have to be a special order (which they were happy to do). Just don't know how much time it will take.