Ok, checked the valves I got last week.
M62 is still the closest match for M42 6 mm stem valve.
N62 valve is even shorter than M62 and there is little gain over M62 valve in any area. It has nicely thinned valve stem however.
5 mm stem S85 and S65 valves seem identical in appearance and measurements. They are somewhat longer than M42 valves and use only one groove collets. I haven't measured their mass but they are quite light indeed. They also have extra cut on valve backside to help flow.
M42B18 (baseline):
33,05 mm
5,95 mm
106,32 mm
M64B44
34,93 mm (+1,88 mm)
5,96 mm
104,12 mm (-2,20 mm)
N62B??
34,88 mm (+1,83 mm)
5,97 / 5,03 mm
100,04 mm (-6,28 mm)
S65/S85
35,47 mm (+2,54 mm)
4,96 mm
111,64 mm (+5,32 mm)

L to R: N62, M62, M42, 2 x S65/S85, S50B30
Clearly S65/S85 valves are superior parts, as they should be. Problems with them I can think of are:
1. Can solid lifters work with 5 mm longer valve stems then original valves?
2. Where can I find valve guides that fit M42 head and have 5 mm stem valves?
3. To get full benefit from lighter weight of intake valves, exhaust valves must be changed too = extra expense
4. New valve spring plates and collets must be purchased = extra expense
I shall study this further.