You definitely want to consider what you need now and what you envision needing in the future. If you don't anticipate needing more than five channels, go with the 5000. The 7140 might be a good fit if you want a little more power (though the 20 wpc likely wouldn't be that noticeable) or think that you'll need those extra two channels in the future.

You'll likely keep the amp for many years more than anything else in your system, except maybe your speakers. Pick the one that should benefit you the most in the long run. The 7700 would be a great amp and provide tons of power, but if you don't need it for your space, I'd go with the 5000 or the 7140.