The norm is 5.25" mostly dictated by a Small Falt Rate Box. This will fit most to all kits, I can't think of one it wont. Now if you are cutting them for Sale I would do this size but be aware, you need to waste. When I cut my blanks for sale I look for the best blank not the most blanks. I have cut a blank right out of the middle of an 11" long blank to get one nice blank instead of two blanks w/ only 50% nice. I keep the rest for my own use and for practicing my casting or dying or burning or what ever I am doing. Now if they are for yourself, dont cut them down. My personal collection has many blanks still their original length. I cut out what I want when I need it, again sometimes cutting right out of the middle.
One last note, I HIGHLY recommend you up the blank to a minimum of 7/8". Try drilling a 13mm hole in a 3/4" blank and you will understand. Cutting them to 3/4" will cut the number of kits that blank will be compatable with. It's like 5/8" blanks only work on 7mm pens for the most part. Same idea w/ 3/4" but 7/8-15/16 is the way to go. When I cut my blanks I set the BS blade to 1" on the outside of the cut. This leaves a 15/16" blank. If it moves I clean it up to 7/8" if not I leave it at 15/16". If you do this and are looking to sell get yourself some padded flat rate envelopes and a lot of packaging tape, as you will only be able to get a few blanks in a small flat rate box.
One last last note, if you are cutting straight grain wood consider Cross Cutting it. You will change to look of the blanks and a cross cut blank has a nice chatoyency that a straight cut will not.
Just a few of my own personal opinions so dont hold them against me......