LK how old was your redline mast? surely they wouldn't have changed the diameter/bend characteristics.
What spacers are you on about? I haven't seen any spacers on my Overdrive.
I'm pretty sure that all manufacturers masts will work with each others sails but to what effectiveness is the question. Until anyone tries the same sail with different masts then we wont get a definitive answer. I suppose a softer mast will spill the gusts better and therefore feel better but wont deliver as much low end drive.