The Sweets article is great, even if the formatting is terrible on that page lol. Personally, I prefer +/- 10% difference between ken and tama. Farther off weight makes spacewalk tricks harder, and juggling too (as others mentioned). It really is preference though, I have a friend in Vancouver who works as a professional juggler/performer, and lately he has started playing kendama. He bought 'the most off-weight setup you can make' off of me: a ~57g Ozora keyaki ken with a ~103g Kusa cherry tama. Almost 50 g difference! He can do some really cool contact-poi juggling style tricks with it.