Re: 135 genoa vs 155 genoa
The key as mentioned for lighter air, is cloth wt. A 135 out of 3ox nylon, ie spin cloth, would be better than the 135 your have I actually use this sail in winds under 5-6 knots, then switch to my 155 to the 15-18 range depending upon air temps, then go to a 140 I have for the 15-22 or so range, then down to a 110 and reefing after that.
If you can get a really light pentax, string style or heavy nylon sail, go for it, but if you get a heavier sail, then it will not be of any benefit at times.
She drives me boat,
I drives me dinghy!