RE: New waveboard
Yes, I'm sure 4.5 sail will be fine with your Kombat 87 and your 85 kg. I'm using a 4.2 as my smallest sail on Kombat 86 up to 30 knots of wind with my 65 kg. Check that old thread as well : http://2006.star-board.com/forum/askteam/read.asp?ID=6179
For your 3 boards quiver choice, I think that a 4.5-6.0 sail range with K87 might be a nice combo with the 6.0-7.0 sail range of your ST115. I'm not sure how a 6.0 sail could be driven efficiently on K79 since you're 20 kg heavier than me, but a 6.2 sail is nice for me on K79 as well as a 6.9 on K86. As for K79 over PA80/86 choice, I'll let Ian (90+ kg) add more comments on that.