How established is your site, how long have you been working on it?
If it's fairly established and older I wouldn't expect a huge amount of change if you were to cut your content somewhat (500-700 is still a lot of words on the page), you might experience a bit of a wobble as google gets used to things, but it shouldn't make a huge difference.
Worst case scenario you can put the old text back and pretend that nothing ever happened.
If you change things and it does make a significant difference it would be interesting to hear about it.
You might want to experiment with your new text first using some sort of A\B testing. That way you'll preserve your current rankings, and test your new text to see if it's going to improve your situation. It's worthwhile testing first before making the switch.
At the most basic end of the spectrum how you have Google website optimizer:
http://www.google.com/websiteoptimizer
but there are some great paid for options out there that do an excellent job.
