This is the question I asked myself, so I took to the internet in hope of finding answers. I did not find any great answers, so I figured it out myself.
Level 1: -
Level 2: -
Level 3: -
Level 4: +1 Cloak of Resistance
Level 5: +1 Magic Armor/Shield, +1 Magic Weapon
Level 6: +1 Ring of Protection, +2 Ability Score Item
Level 7: -
Level 8: +1 Amulet of Natural Armor, +2 Magic Weapon
Level 9: +2 Cloak of Resistance, +2 Magic Armor/Shield
Level 10: +3 Cloak of Resistance, +3 Magic Weapon, +4 Ability Score Item
Level 11: +3 Magic Armor/Shield
Level 12: +2 Ring of Protection, +4 Magic Weapon
Level 13: +4 Cloak of Resistance, +2 Amulet of Natural Armor, +5 Magic Weapon, +6 Ability Score Item
Level 14: +4 Magic Armor/Shield, +3 Ring of Protection
Level 15: +5 Cloak of Resistance, +3 Amulet of Natural Armor, +6 Magic Weapon
Level 16: +5 Magic Armor/Shield, +4 Ring of Protection, +7 Magic Weapon, +6 Dual Ability Score Item
Level 17: +5 Ring of Protection, +4 Amulet of Natural Armor, +9 Magic Weapon, +6 Triple Ability Score Item
Level 18: +5 Amulet of Natural Armor, +10 Magic Weapon
Long answer/Details:
So a lot goes into this. The above chart is obtained by following the rules of 25% WBL to Offense/Defense/Magic, then putting the big 6 is older of cheapest first. It also assumes you always sell the previous item when buying the upgrade, when enchanting to improve quality is probably cheaper. It also assumes you only want a single stat boosting item vs both a mental and a physical, and ignores the dual/tri stat items till MUCH later. You also don't buy both an armor or a shield, and never improve either past +5 quality. This is also a single weapon, so worthless of dual-wielders.
You see the real answer is dependent on the character and their build, and you can manage your wealth far better than this chart assumes. However this gives ME the baseline I was looking for in know that if I'm level 10 and still wearing a ring of protection +1 I'm doing ok, or the fact that my cloak is a +4 means I'm above the curve. So I wanted to share this with you guys in case someone else might find it useful.
Enjoy,
SIN
Some details for DM's
Level 1: -
Level 2: -
Level 3: -
Level 4: -
Level 5: -
Level 6: -
Level 7: +1 Cloak of Resistance
Level 8: -
Level 9: -
Level 10: +1 Magic Armor/Shield, +1 Magic Weapon
Level 11: -
Level 12: +1 Ring of Protection, +2 Ability Score Item
Level 13: -
Level 14: +1 Amulet of Natural Armor
Level 15: +2 Cloak of Resistance, +2 Magic Weapon
Level 16: +2 Magic Armor/Shield
Level 17: +3 Cloak of Resistance, +3 Magic Weapon, +3 Ability Score Item
Level 18: +3 Magic Armor/Shield
Level 19: +2 Ring of Protection, +4 Magic Weapon
Level 20: +2 Amulet of Natural Armor, +6 Ability Score Item
Level 1: -
Level 2: -
Level 3: -
Level 4: -
Level 5: -
Level 6: +1 Cloak of Resistance
Level 7: -
Level 8: -
Level 9: +1 Magic Armor/Shield, +1 Magic Weapon
Level 10: -
Level 11: +1 Ring of Protection, +2 Ability Score Item
Level 12: -
Level 13: +1 Amulet of Natural Armor
Level 14: +2 Cloak of Resistance, +2 Magic Weapon
Level 15: +2 Magic Armor/Shield
Level 16: +3 Cloak of Resistance, +3 Magic Weapon, +3 Ability Score Item
Level 17: +3 Magic Armor/Shield
Level 18: +2 Ring of Protection, +4 Magic Weapon
Level 19: +2 Amulet of Natural Armor, +6 Ability Score Item
Level 20: +4 Cloak of Resistance, +4 Magic Armor/Shield, +5 Magic Weapon
IMHO you should be allocating as much wealth towards improving saves as improving AC. That means that as much money is spent on the cloak of resistance as (armor+amulet of NA+ring of protection) combined. My characters end up with a +5 cloak much sooner than this.
not a bad Standard to have. This would adjust as follows:
Cloak of Resistance at Levels: 5, 8, 10, 12, 13Magic Armor at Levels: 5, 10, 12, 15, 17
Ring of Protection at Levels: 8, 13, 16, 18, 19
Amulet of Natural Armor at Levels: 9, 14, 17, 18, 19
With this standard I think it would be best to invest closer to 30-40% WBL to protection.
Edit:
You could instead aim for a "Resistance > AC" method and do this:
Cloak of Resistance at Levels: 4, 6, 8, 9, 11
Magic Armor at Levels: 11, 12, 13, 14, 16
Ring of Protection at Levels: 11, 13, 15, 16, 17
Amulet of Natural Armor at Levels: 12, 14, 15, 17, 18
Its probably worth noting that some slotless items fit in pretty well with the big six. Specifically getting 2 Cracked Pale Green Prism and 1 Normal Dusty Rose Prism ioun stones.
I would fit in +1 to attack between belt (str or dex) +2 and +4, +1 saves between cloak +2 and +3, and +1 AC between Ring of Protection +1 and +2. You can also slot the Dusty Rose into a wayfinder for the resonance bonus (+1 to CMB).
I used to consider Jingasa of the Fortunate Soldier to be in that camp, but it was changed from a Luck bonus to a Deflection bonus and the crit negation was changed from 1/day to 1/ever a while back.A wizard should get a +6 con belt at least. May not be high on the priority list, but GMs tend to put in some (nearly) unavoidable damage for 'plot' reasons.
Absolutely adding those stones to my Big Six buy rotation.