It would be interesting if someone published the 'effective browser technology guide' which defined the set of things that would look the same on all browsers. It might end up with just CSS2 and tables though :-(
But it can't tell you if things will look the same, and it only goes back as far as ie8.
Examples:
http://www.positioniseverything.net/explorer/doubled-margin.... http://www.positioniseverything.net/explorer/floatIndent.htm...