Link pleaseMarshall Vintage G12 is a 65 watt speaker. It has a very large magnet, very different than the Vintage 30. If you have an opportunity do a search in the forum, I have a post here on it, I also have sound clips of one stack with the Marshall Vintage G12 against a stack loaded with Vintage 30's. Both are amazing but my go stack is loaded with these Marshall Vintage G12's.
Vintage 30's = 60 Wattts
Marshall Vintage by Celestion = 65 watts
Dr. Decibel at Celestion is great at responding to emails, Dr Decibel Archive - Celestion. Thats how I learned about my mine, if you need additional information he can most certainly help. Also, if @BygoneTones see this he can help, another amazing resource on all things Celestion.
Bygone Tones - Vintage Guitar Speakers & Cabinets