Custom rom questions

I currently have an iPhone and am looking at potentially getting an Android device, and I am probably thinking way too far ahead, and obviously I don't know the specs of the future devices, but I am looking at comparing other phones to the Nexus series, from a custom roms perspective. I would not buy a Galaxy Nexus now because I expect a new Nexus device (or even multiple ones) this coming fall, which is why I mentioned future devices above. Looking at the history of Nexus devices, it seems that Nexus devices, although the Nexus devices obviously provide quick official updates and having the advantage of the OS being designed for their specific hardware, aren't exactly top of the line in the spec department. So while it's appealing to have the official Google phone, I am interested in some of the other top-end devices (again, likely future devices). am not afraid to root and install a custom rom. I installed ICS on my touchpad, and didn't have many problems with that. So I don't care if I have to spend a few hours every once in a while to install the next update.

So, with all that out of the way, I have a few questions on the custom roms world:

1) How long does it take for custom roms to be released? Keep in mind, I am talking about the top of the line $300 on contract devices, not the cheaper options. I assume that those devices likely have better developer support. Does it depend on manufacturers and locking their boot loaders? Do different carrier phones have different delays? (I would almost certainly buy an AT&T phone right from AT&T for LTE, instead of buying the international version.) Is it days? weeks? completely variable?

2) How is the performance? Are there typically noticeable missing features, or buggy features, such as the camera, wifi, audio jack, etc? If so, how quickly are those addressed? Are they much more buggier than stock Android?

3) I hear a lot about how the Galaxy Nexus is still a better option than other top devices because Jelly Bean makes it run so smooth or whatever. But if I were able to relatively quickly to say Jelly Bean (or Key Lime Pie or whatever), I don't really care if the Nexus device is better performing for a week. So if I could relatively quickly update to the newest OS on my other device, would that make the other phone perform better than the Nexus device, or is the fact that the OS likely has performance tweaks for the Nexus hardware outdo it?

Lastly, I would buy a top end device like the One X or GS3, which presumably should have pretty good developer support. Obviously if Google does actually release multiple nexus devices, there may very well be a Nexus device with top of the line specs, it's anyone's guess. But the assumption of my post is that the new Nexus device will likely be very good, but not the best (for example, the 5MP camera on the Galaxy Nexus).

Thanks in advance!