For Seduction, it's 60pF, IIRC. Add that to the tonearm wiring and you have your total number. You can measure the wire/cable capacitance if you have a meter capable of measuring low capacitance accurately. A lot of meters dont but they do make meters just for measuring LCR or even specifically for measuring capacitance. You can do a search on the net and probably find the capacitance of the stock Rega arm wiring. Ive seen it before. I doubt that it's higher than 150pf and maybe closer to 100pF. I wouldnt get too obsessive about it though. As Grainger suggests, you can add capacitance but you are probably in the ballpark as is for most of the modern MM carts. For example, the popular Ortofon 2M series all "want" 150-300pF.