Hi Spike, thanks for the trust in our brand with your quiver there already!
First q - well the Blast 100 would feel more like your bigger Blast, but actually quite a bit faster/more manoeuvrable, as quite a bit narrower. For Flat water blast/speed/control, for sure better than the FW.
If you want to improve your wavesailing, then why not get a Mamba yes - or as good option going fwd, perhaps a 2020/21 FreeWave 95L, to replace your 105 and double up as wave/flat water blaster?
But if you want somehting more wave oriented - then Mamba 84/Stubby 89 also a good call?