I've found that calculator
to be a pretty good guide overall, but I think the calculations for board size are a bit dated. The biggest change in board design the past few seasons has been adding width to get more planing surface, rather than length.
I'm about the same size as you and unless it's an Ocean Rodeo Mako, that 150 you've been learning on strikes me as rather large. While it may be good for learning, as soon as you're riding a bit more confidently upwind, you're going to have trouble holding the board down as you build apparent wind and power in the kite. But then there are guys around here who ride big boards with larger kites in 20 knots. I can't understand why. My 142x42cm Nobile NBL was an excellent platform for progression; I intend to keep it around for other people and when the wind drops a bit.
I relate the story of how I built my quiver in this reddit thread
. I feel as though I have a bit of a gap between the 13m and the 9m. When the 13m dies, I'll probably replace it with a grunty 12m--which seems to be the most common size in Toronto, then 13s and 14s, and finally 11s. I don't see too many 10m kites here. They seem to occupy something of a nether region for the average size rider: Too tiny for the average conditions, too big for when things pick up.
If it's under 12 knots, most people here just don't bother. That said, because of PBK Paul, we have a fairly large contingent of people who are in love with their Flysurfers and weird Flyrace boards. I don't know what their lower threshold is, because I'm not usually at the beach when they bust out the 21s. I'm hoping that between my cheap-ass foil and low-rocker/high-volume, quad-fin surfy that I'll be able to get out in 8-10 knots, maybe less. We'll see how that goes this summer.
Hopefully that gives you some insight, maybe I'll see you on the beach!