Well, unless you've gathered (literally) millions of downloads while free, you won't see much (if any) of your free momentum convert to the paid charts, tbh. In fact, usually after a few days of an average free campaign, you're already spiraling down the free charts... and that's if you were fortunate enough to do well in the first place.
If you can hit around 400-500k downloads then you might
see a tiny hint of a boost for a few days, but I still wouldn't count on it.
That being said, if you can generate a few 100k downloads, you will likely see a nice little boost in revenue due to IAP purchases at least.
But you should just take it as it comes... figure out what to do once you see how well your free campaign goes.
And again, as always, in the App Store anything can happen, this is just from our experience (we've done quite a few free campaigns over the years)