Hey andjroo,
I reckon youll be fine on the 105, I progressed from a 131 carve to a 89L '08 kombat (Im 63kg). If you can waterstart (uphauling might even be possible on the 105) and rip along alright, it's not that big a jump, thats where I was at when I bought the kombat.
Some things I found different, as already mentioned it'll accelerate onto the plane and swing into corners quicker, loose speed a lot more rapidly and feel much looser/skittish than your big board, the hardest thing I found was how willing the nose of the kombat was to sink compared to the carve, once I learned to move straight back on the gusts it was all good.
I actually learnt to carve gybe on the smaller board too, because it reacted directly when I moved my foot over, and having to balance the rig in relation to where the board was made me carve the board all the way through too as opposed to the big board where I could put the rigs weight and my weight over the board, I couldnt get it to go past downwind.
I've finished my novel