Hi Wave Dave, depends a little on your sail range- so if you get a 6.7, then the 117 would make sense - it is 67cm wide, quite manoeuvrable and will give you an extra wind range in the lighter air. Or, if you think you may go bigger on sail size or really want to push the light wind envelope, then the Blast 132 at 71cm width is also an option. The Freewave 105 you have is 63cm wide, so enough difference to both of the Blast sizes.
Both boards a good investment, I think it's just a question of the needed/expected wind range. Obviously the smaller 117 will be more dynamic and feel closer to the FreeWaves.