Also on the subject of beef - how thick should I be slicing and how much to serve 6 plus leftovers. My logic would suggest 4+kg but maybe that's just me being a fatty. My local (fancy) butcher's price list suggests that's around 100 quid of beef. Sound legit?
CYOA
Done this one before - it's bloody lovely, and works very well as with most foodlab things http://www.seriouseats.com/2015/12/step-by-step-food-lab-reverse-sear-prime-rib.html