A dimension of 3000 largest size x or y should cover all common caching cases for SVG icons and web app elements, but not caching large vector rasters that would exhaust the cache.
This limit is a royal 36MB/element (3000x3000x4) as cap (if the SVG is square). This avoids performance regressions when repeatedly scaling large vector images, but also allows for large SVG backgrounds to be cached.
It allows for the bad practice of slapping a large SVG on a site as html background, considering they are likely, even when using large sizes for "responsive" layout, not going to exceed 3000 px in the largest dimension (and if they do, the web designer needs to be slapped with a big trout).
wolfbeast
Matt A. Tobin