well,  Regular flex for speed 65 - 90 mph, Stiff flex for speed 95 - 130 mph, Extra Stiff shaft for speed 130 - above.

once again You can use it only for a standard measurement. actually one shaft and another, also year of production will make a different about it's stiffness. for a sample; Mizuno Techno flex 5770 shaft from 1995 Regular flex is the same as Mizuno Quadra Stiff Flex.  Graphite design Tour AD Flex S as same as  Honma ARMRQ UD49 5 stars Flex R.

if you want to buy driver or irons or fairway...it would be better you go to custom fitting and get fitted shaft that best on you swing character.

No.  That's not true.  Please go to fitter to find out your shaft stiffness.  It includes your downswing shaft load as well.

Just because you have a high swing speed does not mean you need extra stiff shafts.  You also have to factor in shaft load on the down swing as well as swing tempo.  For example, there are players with a very high clubhead speed but don't need or play extra stiff shafts because of a long smooth swing which produces less shaft load on the downswing but still produces tremendous clubhead speed.  Best bet is to go get fit with an instructor that uses a launch monitor to get the right shaft and shaft flex that best suits your swing.  Best of Luck!

IMO ball speed not club head speed is a more important factor to consider when selecting a shaft.  There are many other variables to consider to give the player their preferred trajectory, feel and performance that they are looking for in a golf club.  As a general rule, softer and lighter weight shafts work well to increase launch and backspin while heavier and stiffer shafts help to lower launch and reduce backspin.