The difference between 70mm and 85mm is so minimal that I don't get why the option is between an 85L and a 70-200/4 IS. They're two entirely different beasts.
Looking through your Flickr stream, your main subjects seem to be landscape and urban/street and what I'll call 'travel photography'. The focals in a lot of your shots tend towards the wide (ultra wide, in fact, I'm guessing you had a Tokina at some point?), equivalent to 16-17mm on full frame, as well as plenty that sit comfortably around the 24mm mark.
How much do you use your Nifty Fifty? Do you really, really, really like the focal? Or do you 'just' like the fact it's fast? Ever looked through your shots' EXIF info to see what focal length you spend most of your time on? Have you ever 'spent time' with glass longer than 70mm?
I have relatively similar tastes in subject matter (more landscape and candid portraits for me, though, less street), but people 'see' differently. And working with full frame changes things a lot - the 5DII is an absolute beast of a camera.
My suggestion: if you can afford the 70-200L right now, since you can get a cash back, why not just buy it. Gives you a great cover and one of Canon's best bits of glass. Worst case, you should be able to sell the 70-200 at pretty much zero loss down the line (i.e. after the cash back offer is no longer a factor), as it is by far one of the most popular bits of Canon glass out there. Or you may discover you really, really like it. If you can afford the financial hit, it's a no-lose situation.
Most importantly, however, go play and shoot with your new 5D. Learn its strengths and weaknesses. Experience how your existing glass works on camera. See what focal lengths you end up using. Find out if you want more reach, less reach. For example, I find 50mm to be 'ok' on crop, but nothing thrilling, but I really do like it on FF (see sig, self-evident). For walkaround/street/close quarters people, however, I prefer 35mm. And I tend to 'see' outdoor candid portraits at 135. So it made sense for me to get those primes. I still want a 24LII, or better, a Zeiss 21mm to round out the 'primes' collection, but I'll admit it's a 'luxeprobleem' 
EDIT: reading your reply, maybe consider the 135L. Only a little longer than 70mm on crop, very, very sharp, lighter than the 85L, faster focus, and I think it really has that magic look to it.