You would think the curved blade would help you dig into shallow dips slightly better, but in practice it seems not to make much difference.
For chasing a ring I would suggest a knife around 8", it puts your hands closer to the blade and lets you have a little better control. For hogging bark and sapwood, a larger knife is good for better leverage and keeps you from busting knuckles.
I scarf up used drawknives wherever I go, its a sickness.