I currently have the vsl synchron stage reverb for the next 30 days and i also own the full spitfire reverb. Maybe someone is interested in the difference inside of a video.
Current test stats:
VSL reverb requires about a third of cpu compared to spitfire Reverb, however Spitfire reverb is more suited for soundtracks and provides longer and more detailed sound responses compared to vsl which sounds really soundstagy. I personaly would prefer spitfires reverb also because you have way more options such as changeing panels and more freely Positioning of instruments on a virtual stage even when this ir simulation takes way more cpu