this is a good site that if you put in make model year etc will give speeds at any gear/revs at standard gearing and also any front/rear sprocket combo you enter- gives good idea what any changes will do what once you have a starting point- -
i got small select of 2fronts + 3rears and made table of each combo at just below red line so from here so could quickly see difference they all make
link below;
http://www.gearingcommander.com/