Several weeks ago it came to my attention that some people were having overheating problems with their G540 when running four 3.5A motors. I ran an experiment last week to determine the best way to heatsink a G540 and how it will react when all four axes are being run at 3.5A simultaneously. The results are in the link below.
If you do not like reading things like that, here is a summary of what I found: If you have air flowing over the G540 while it is running it will perform just as well as it would with a heatsink attached to it. Make sure you have air flowing over the back of your G540 and you should not experience problems with your gecko overheating.
Here is the link: http://geckodrive.com/upload/G540%20...Experiment.pdf
If you have any questions about this, just let me know.