Hi RandomGuy! Here is my latest experience with an MacBook Air 13-inch with 8GB RAM, 512GB SSD and an i7 processor, upgraded to OS-X 10.11 and Xcode 7.0.1. These two updates blew my Swift development work out of the water. It appears that both OS-X 10.11 and Xcode 7.0.1 are memory hogs. The industry use to refer to Microsoft software as "fatware". Looks like Apple is following suit. My computer was in an CPU-intensive state as a result of attempting to run Xcode, my guess, doing a lot of virtual memory swapping due to the high memory requirements, unpublished, for OS-X 10.11 and Xcode 7.
When I launched Xcode 7.0.1, the fan starts humming and the CPU-utilization, as measured by the Activity Monitor, shows 0% Idle Process time. I simply cannot do any Swift development. Moreover, in non-Xcode work, the above system is also useless. I launched Pages to print a 4 page technical paper that describes an algorithm for doing file comparisons. Again, the fan kicks on, the paper is printed, obviously more slowly than under Yosemite, as the Activity Monitor again shows 0% Idle Process time. After this, I wanted to shutdown via the shutdown menu. Because of the intense CPU-utilization, I could not get a response to my software shutdown request. I had to had to push the "PowerOn" ("PowerDown" in this case) button to shutdown the system manually. Note that I had no such problems with the Yosemite 10.10.x and Xode 6.x updates.
It looks to me that the Apple Development Organization ran out of schedule and had to ship before being able to: (1) perform regression testing (El Capitan vs Yosemite), (2) performance testing and (3) memory trimming its software requirements for OS-X 10.11 and Xcode 7.0.x. I have five Bug Reports about these issues in at Apple now - all unanswered at this point. I have also written two letters to Tim Cook bringing these issues to his attention, again, no response. I hope I am the only software developer experiencing these issues with OS-X 10.11 and Xcode 7. If so, count your blessings, If not, you understand my frustration.
I remember the Microsoft Windows Vista debacle several years back. It caused Microsoft several years to recover from that. It looks as though Apple wants to follow Microsoft's path in this regard. If I was an Apple stockholder, which I am not, I would be asking a lot of questions about Apple's software development organization and how it is being run. It appears to me that the software development schedule is determined by Apple's annual hype show in San Francisco. Just a guess but that is the way it looks to me after seeing similar situations during 50+ years of software development with other computer manufacturers including ones that I worked in. My advice to Apple: cut the functionality to make schedule or cut the annual hype-show. My guess the latter wins in the Apple Marketing organization and software development has no say in the process!!! Watts Humphrey's classic book, "Winning with Software: An Executive Strategy" makes a very bold statement when it says "[Software] quality is more important than schedule". That is in engineering terms, tradeoff schedule, if necessary, to produce a high quality software product. I don't see that software management principle in operation at Apple and in most other software organizations I am familiar with. In that regard, Apple has plenty of company!!!