Can someone tell me why SVGs are gigantic while first loading? I often see this even at modern connection speeds.
You're lucky. Last designer I asked to provide a SVG image had obviously exported from a vector drawing tool to a bitmap, AND THEN converted to SVG. So you kinda had a whole SVG object for each pixel.
It never occurred to him that a 40 MB SVG file might indicate a problem (when the point of having a vector format was partly to save memory).
I wonder how big can the SVG DOM be in browsers before things start to get painfully slow
Usually happens with SVGs whose internal dimensions differ wildly from the display dimensions.
e.g. Internal canvas of 1000px x 1000px, display size of 10px.