As you have 340's, the answer is right in front of you
Read the documentation (and if you don't have it, you can download from
www.geckodrive.com) and read up on the multiplyer function. It will effectively turn your 1000 line encoder into a 1000 line (multiplier 1), 500 line (multiplyer 2), 200 line (multiplyer 5), or 100 line encoder (multiplyer 10).
Also remember that as the line count goes down, so does your resolution so it is a tradeoff between speed and resolution!
For my purposes I set up a simple spreadsheet to show the various tradeoffs and then set my geckos accordingly. In my case, having 1000 line encoders, I used a 2 multiplyer and get satisfactory results.
