I'm looking at getting Ka Koncepts 2016 or 2017 to replace my aging 2009 Hotsails Gps 6.0 & 6.6 and my 2011 Tushinghm X15 5.8 and 6.3 (I kept my old sails to use as they weren't worth anything, but handy to have as spare). My largest sail is a 7.8 Overdrive R6 and I won't replacing this any time soon.

Boards: 2014 110 Fanatic falcon and 2006 CA SL55 high wind slalom (due for an upgrade to a board of similar size)

Use: Powered up slalom sailing and speedsailing in harbour conditions.....but not racing at this stage.

I was considering getting 5.4 and 6.6 Koncept. Would this be an ok Gap? I like the idea of easily choosing a sail/board combo when I go out.....its light, medium or strong wind.

Also the smaller Koncepts have a deeper foil, so I assume they are grunty for their size? I weigh 70kgs and some times do get over powered on the 5.8 & 6.0. Would the 5.4 allow me to sail in the slightly higher winds that my 5.8 or 6.0 OR due to fact the Koncepts are grunty, should I be looking at the 5.0?

I use Koncept 5.8 2016 up to around 30 knots if it's not too choppy. I love this sail and I've done my best speed and alpha pbs with it. Koncepts are very light and you don't get overpowered easily. From 5.8 to 6.6 is the right gap for me, my weight is 76. I also have a 5.4 2014 which is good too but used much less. It really depends on the conditions you will be sailing and what you can find available.
In 2016 I used the 6.6 9 times, 5.8 9 times and the 5.4 2 times, never used the 5.0
In 2017 so far I used 6.6 6 times and 5.8 4 times
Hope this helps

I am 72-75KG and mostly use 5,4m, 6.2m and 7m these days. In a genuine 30 knots for speed sailing on flattish water, I use 5m or 5,4m Koncepts. 30-35+, definitely the 5m unless conditions are perfect - with weight in vest!

For what you are doing you are on the right track. If it is harbour, open water choppy, in wind where you would want the 5.4m, you may be a bit out of control and better off on small freeride gear and a wave sail. But if you have the skills and/or better water conditions, the 5.4m to 6.6m is a reasonable gap.

I'm running a SL 66 (110L) with a 7.5 and a SL 52 (82L) with a 6.6 / 5.8 at 85kg I would look at a 7.5 and 6.6 if you like being fully powered up with a 5.8 as a third option for 30 kts +
Koncepts do have a large wind range with the high end being very stable

Big thank you for all your comments

I ended up ordering 2016 6.6 and 5.4 Koncepts that were on sale. After reading your posts I was leaning towards a 5.8, but they were out of stock when I came to order. I was considering getting a 6.3 instead of the 6.6, but the 6.3 could be getting on the small side for my 110L

My 7.8 will easily get me into the power band of the 6.6, I know this as I was having a blast fully lit on the 7.8 110L, 44cm Venom. I was comparing my speed against a sailor who was using a 2010 6.0 Koncept and ~100L slalom board. He would be 5-10kgs heavier than me and was planning most of the time.

Time will tell if the 6.6 to 5.4 is an manageable gap and as was said, the conditions maybe too rough to get the most out of it at some of the places I sail. I do have a 77L FSW and a 4.2 which I used in really choppy conditions, this has the added bonus of being able to sheet out when the big gusts come through and the board remains stuck on the water

The board I believe is going to get me up my personal speed ladder is a 220L Fanatic Viper 85 .......... This has been used as a SUP to scout out flat water spots and have found at least one spot that at certain tides, will give me flat water on a very broad reach in a SW wind which typically blows 25 to 35 knots when it comes through. I hope the 5.4 can be put to good used there