I am going to chime in here.
I am on the same page as the people who are asking to please answer the question as opposed to judging the asker for using “old software” or wanting a new operating system, etc. I have my reasons for wanting to upgrade to El Cap but still use FCP 7. It’s because I want to use other software that requires the new operating system. So all of this presumptive dissing is really unhelpful.
My gratitude to those who did answer the question. I’m still unsure of what to do but I may go for it. For now I feel like I have two computers that are compromised b/c neither of them have all the software I need them to have. So it goes. Ironically. Because my purpose for buying a 2nd computer was to be able to work from home and office. Now I can’t do either unless both machines are in the same location. Fortunately one is a laptop.
OK. If anyone has more input that actually answers this very important question (to some of us, anyway) the more info the better! Thanks!!