I kind of over-did the modification, but it works great. I would prefer a down-spiral or at least a down-sheer bit, but the bigger diameter makes up for it, at least some. 5/8" diameter and a full inch of cut length.
If you can get by with less cut length, Shaper Tools has just come out with a 16mm bit, both diameter and length, with an 8mm shank too.
Maybe 3 flute too? I haven't seen one in person, but it looks interesting at least. They sell it as a bottom flattening cutter for pockets, using the Origin, but it could certainly be used for other things too.