[Aerich]

When you dual class depends on your party composition and what you forsee that character doing. If you want to have an end-game hero, dual over at 12th or 13th level (preferably 13, for the extra 1/2 attack per round). Just be warned that you will not regain your ranger class for a looong time. It's probably not the best tactic on Core (normal) difficulty if it's your first time through - it makes the game harder throughout and a small bit easier at the end. All this doesn't mean that a R/C that duals at 7 or 9 will be weak at the end; far from it!

If you have plenty of tanks (warriors) and healing/buffing clerical spells in the party already, you can get away with dualing later. If you don't have a cleric (not counting the R/C), you probably want to dual sooner to get a decent Turn Undead ability and access to the cool clerical spells. If you forsee the R/C as a late-game tank with buffing spells, dual later.

One benefit of attaining a medium level (6) in Ranger before dualling to Cleric is access to first level druidic spells.

When I dual fighter-types over to another class, I usually wait at least until 7th level. It costs less than 100 000 XP and gives 2 more proficiencies (at 3rd and 6th level) and an extra 1/2 attack per round (at 7th). 9th level gives another weapon slot and the max HP you can get by die roll as a warrior, but cleric is not really much of a step down. If you have an 18 Con, it's probably worth it to keep the ranger until reaching 9, for the warriors HP bonus for Con.

With a party of six, I would dc at 7th level or 9th level (if you have another healer). I don't consider the improved Thac0 and slightly higher HP worth the huge experience it takes to get past level 9. Any such improvement can probably be made up with priest spells anyway.

I'm also a notorious priest-lover (for the game, not real life [img]smile.gif[/img] ) so earlier access to priest spells is a critical plus for me.