With today's sensors perhaps the 70-200 f4 IS would be something to consider -- much lighter, said to be sharper than a sushi knife, and also excellent IS -- with an L build.
It certainly is a substantially more compact lens Dave. I've never used it myself but see a lot of folks here being very happy with it. I've used that extra stop of the 2.8 on the larger lens to good advantage under really poor lighting, but I agree that today's sensors are leveling the playing field a bit more.
However you can still get some great background isolation with that f/2.8. The f/4 is no slouch, but you can see the difference
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... guy is whining... well praising about 50gram difference between 70D and 7D. Lets say about 90% of his messages ( I really havent count them) 
