My advice is to use grand charms that only just qualify for + skills. Those affixes are actually rather lower level than you think, [wcip] Angel
High level charms like your one allow more affixes but really, is there anything that comes close to being so useful as +skills?
A higher level charm with more affixes available gets +skills less often than one of the optimum ilvl 50.
Ilvl 50 gets +skills 1 in 21.9, ilvl 99 gets +skills 1 in 23
This is based on higher level charms unlocking the following prefixes:
alvl 55: Lucky 8-12% magic find
alvl 67: Serrated +3 max damage
alvl 75: Bloody +3 min damage
You might well feel happy to add Lucky to the mixing pot but I doubt many people will be pleased to see +3 damage when they could have re-rolled +skills
The affix calculator here lets you see what is available:
http://www.diabloii.nu/affixcalc/
This site lists area levels. In Nightmare and Hell area level = mlvl = ilvl for normal, non-boss monsters, with alvl = ilvl on charms:
http://home.t-online.de/home/320071388834-...F_Guide_ENG.htm
For re-rolling grand charms I'd suggest level 50 - level 63 areas. A level 64 area could have a boss drop a level 67 charm which would be sub-optimal. If you're rich enough to scoff at the idea of a 10% mf grand charm or at the idea of a skills charm without a high +life suffix just use the links to develop a different strategy
By the way with small charms I rather like the very high level affixes so for them going high is recommended