Gary, you may disagree with me, I'm fine with that, but posting comments like this really isn't helpful. Fine to state your case,
but not good forum etiquette to bash other posters.
I am a professional unit stills and BTS photographer covering film and theatre, more to the point, I get paid for it and I HAVE to get my shots for the client. I can assure you the musicals I have covered are not slow in action. I run with two cameras, one with my 24-105, the other with the 70-200. As with sports, which I have also covered (photos in the press, etc.), there will be low light situations. To shoot reliably at 200mm and with no IS the shutter needs to be at 1/250th or better (not 100th), with IS I've shot as low as 1/20th and still had usable shots.
There is more to shooting sports than the fast action shots, there is general reportage.
I can guarantee the IS makes the lens a lot more practical. Before getting the IS version of the lens it stayed in my bag far too much of the time which isn't great, even for such a reasonably priced lens, but when I've invested in gear it has to earn it's keep.
The image quality of the IS version of the lens is noticeably better and it is sharper. It focuses more reliably and doesn't have the "needless refocus to out of focus" problems I had with the non-IS version.
The 2.8 is twice the weight of the f4. A massive 1.5 kilos for the 2.8. Fine for a few portrait shots, but when you are on an event for hours at a time (I've been on shoots for up to 12 hours) the weight of your gear becomes an issue - especially using two cameras. The difference in bokeh and separation from the 2.8 to the f4 is noticeable, but it's not THAT big a difference.
OP, good luck with whichever choice you make