I think binary logging might help if you aren't doing it already, but if the frequency and content requirements are as you've described, I think you should be looking at logging into a database using PAC Display Pro or OptoDatalink.
Edit... I just re-read. What frequency do you need to log at? Make sure you set the "refresh time" to that time. It sounds like you have the refresh time set very short.
You can create a short refresh time supertrend for graphical display that is really responsive (with no logging), and a second hidden supertrend chart with a longer refresh time for lower frequency logging.