That would depend greatly on whether or not you are doing client side rendering, and the client device being used. Here is just one example of a
site that uses leaflet heavily, but they mix it with geoserver, arcserver and client-side rendered geojson. In my own work I am using only client side rendered geojson and have found the major limiting factor to be the loading of the icons for points more than anything else. I am only loading maybe 3000 static features, however. Also, for loading geojson or other client side rendered data, limiting the amount of fields helps with speed. Of course if your clients are all using desktops linked with high speed internet, you have much more processing power and bandwidth to play with.