A belated "thank you!" for this. I haven't had time since last week to look into this, but would still like to try something out.
Is there a way I could instead temporarily access the old stats by renaming the tables and then setting them back, just to get the last two months of audience data? I actually like how much better SlimStat is performing now, and not timing out trying to access a huge database. Once I have what I need from wp_slim_stats_3, I could get rid of it.