The biggest reason to convert a stock frame to 650b is to create more clearance for bigger tires. Your standover doesn't get affected much because of the bigger tires. A "700c"wheel is 622mm while 650b is 584.That's only a difference of 19mm in radius, if you substitute 40mm tires for 28 you regain 12mm. The only technical thing to worry about is the break reach. Mine is here:

http://simplecycle-marc.blogspot.com...and-mixte.html

Marc