This is a common recommendation on the forums and elsewhere to increase LPM. Here's a tutorial that describes the process:
(4:30 if the video doesn't start there)
In short, after the project has run for some time users adjust the engine selection to only use engines which have been verified as per the verified sites list stats. Or to remove engines which haven't been verifying often. Naturally this can make a project vastly more efficient. But it's also incredibly time consuming to navigate the engine list this way. The engines aren't listed alphabetically and the verified site list stats don't correspond to engine order either. This process is easily the most time consuming aspect of using GSA for me.
It would be nice if this was automated. I know it'd save a lot of time on the maintenance of ongoing projects for most avid GSA users and doesn't seem too complex to implement. It could be its own option on the engine select e.g. uncheck engines that have not been verified (more than X times).
If something like this is already easily done then I'd love to know, either way I love GSA! Keep up the good work.