LOL. Yes, I knew your knife was a 240. By 10*, I trying to say your bevel angle looked like 10 degrees (judged by its width). I wasn't commenting on the knife length. FWIW, the reason Japanese makers make knives in multiples of 30mm (210, 240, 270), is their traditional unit is the "sun" which is 30mm darn near. More often than not, even though manufacturers express lengths in millimeters there's really no standard of how to measure a blade and there can be a lot of variation. Also usually, the more handmade, the more variation.
Yes. Finding your own angles is a good thing. You paid for the knife and went to all the trouble of learning how to freehand. You might as well have the edge which suits you best.
There's always a tension between durability and absolute sharpness. The more acute the angles, and the higher degree of asymmetry, the sharper the edge. However, really steep, asymmetric edges do not hold up particularly well. The thing to do is try and find the edge of the envelope where you don't have to do so much maintenance it's an annoyance.
In terms of the type of knife you're using, that usually means a 10* edge angle with a 15* micro bevel on top. There's nothing particularly magic or "right" about those numbers -- it's just that lots of people find it splits the diff pretty well.
Asymmetry is slightly more complicated. Japanese knives often come ootb asymmetric, and western users often assume that the degree of asymmetry was the manufacturer's intent. Not so. One good way to establish more or less asymmetry is by starting on whichever side you want to move the edge from, sharpen to get a burr, then sharpen the other side, only until you get a burr -- WITHOUT trying to match the number of strokes. It's in the nature of burrs to require more material removal from the first side -- which gradually shifts the symmetry.
If you're left handed, you want to develop the left side (holding it by the handle and looking down the spine); and if you're right handed, you want to develop the right side. Fortunately, it's easy to see what you're doing. You can measure the degree of asymmetry fairly accurately by comparing the width of the bevel on one side to the width on the other. 80/20 (righty) means the right side bevel will be four times wider than the left side's bevel. 70/30 -- which is very common -- means the right side bevel will be roughly twice as wide as the left. Note that it's more important to be able to make a visual check than it is to hit a precise level of asymmetry.
Like 15/10 degree bevels, 2:1 (aka 70/30) is a good compromise between durability. You have enough asymmetry to really make a difference, but the edge is still robust enough to true on a rod hone. Anything more asymmetric is too weak for a rod which will probably create more problems in terms of chipping and rolling the edge off true, than it solves.
If the knife will be used by both a left and right handed user, you might want to consider 50/50 as asymmetry can cause the blade to "steer." If one or the other user has a sufficiently good grip to prevent steering anyway, you can still go as far as 2:1. But any more than that will tend to push the knife too far from the wrong-handed user's claw and make small precision cuts like julienne and brunoise difficult.
More than you wanted to know?