I think ZW is correct, but that CPM has me confused. I wish I had Tom Wishon's shaft software so I could give you a better sense, but I do have a list of 23 shafts that were posted on GolfWrx, which are place in order first based on butt stiffness, then on mid-shaft stiffness, and then tip stiffness.
The least stiff butt measurement on that list is TW Golf Plus High Flight Graphite regular, which has a Butt Frequency of 297. I notice, though, that this Butt Firmness is described as "Medium," so maybe there are shafts that get as soft as 263 (but that would seem very soft to me based on this chart).
FWIW, I think there are also different ways of measuring CPM and the measurement depends on the length of the vice being used and the weight used on the tip. For example, here is a post that was taken from the same thread as the tables above:
"Here are the cpm ranges that helped me figuring out the relative stiffness :
-----------------------BUTT (36/31)------------- MID (26-21)------------TIP (16-11)
X-Flexible----------<210 -----------------------<320---------------------600-630
Flexible-------------210-220------------------- 320-330-----------------630-660
Medium------------ 220-230------------------- 330-340---------------- 660-680
Firm-----------------230-240------------------- 340-350----------------680-710
Stiff------------------240-250-------------------- 350-375 ----------------710-770
X-Stiff--------------->250------------------------- >375 --------------------->770"
Notice that these figures make no sense in relation to your 5.0/263 marking and it makes no sense in terms of the tables I have. Obviously whoever posted this is using a different method of measuring CPM.
