Yes you can get away with 10% leech on an Arcane mage, but it limits you on what you can do. I had around 10% at one point and wasn't able to sell runs in a timely matter. Now that I'm over 30%, I can pull a whole instance if I wanted if I bosses weren't in my way. My suggestions is to get as much as you can, can never have too much. Especially with how hard 110s hit in world PVP and how high miss chance is on casters. That way whatever attack does last, the leech heal with say 40% makes up for the 3 other misses