Greater than 600 and you want to snuff it? I had a mid-pole on a 6.0 that we were snuffing a 400 or so Smyth spin. PIA! Maybe it was the snuffer head size since it always seemed a little small. I think it was a Prost. So from my experience you may want to make sure it is a big diameter head. I think both the heads entrance and exit need to be big. Also, you may want to think about how long your bag will need to be. What are you dimension that you are working with like luff length and foot length and how long your pole is.