About reaching DC of 50... There is a way... A charisma based Protection domain cleric way... All you need is 30 levels of cleric, +10 or better charisma modifier (works well with turn undead abilities) - and just hit that Protection Domain Power and you get to run around untouched, unmolested!

You could even go higher than 50, by the way...
As for an arcanist reaching as high caster level as possible... Wizard 6/Blood Magus 6/Archmage 8/Shadow Adept 10.
+2 Int race... ( or +2 Cha if going Sorcerer... )
Ability score:
20 (Base intelligence)
+ 7 (Ability score increases)
+ 2 (Spellcasting Prodigy)
+ 4 (Fox's Cunning, or Item)
+ 3 (Great Intelligence feats)
= 36, modifier of 13
Caster level:
29 (Without practised spellcaster)
+ 3 (Archmage Spell Power)
+ 3 (Shadow Adept Spell Power)
+ 3 (Bloodmagus Blood Component and Blood Seeking Spell)
= 38, which gives us a +6 Epic spell caster bonus.
Thus... your DC could be:
10 (Base)
+ 13 (Ability modifier)
+ 9 (Spell level)
+ 3 (Epic Spell Focus Necromancy)
+ 6 (Epic Spellcaster bonus)
+ 2 (Shadow magic)
= 43
Have I forgotten something? Well, if you can convince DMs to grant you Spirit Shaman's
Blood Magic feat it could be another +4 to your spell DCs... But the feat no longer lists magical discovery on the forums, so not sure if this is still a possibility. Hence, you used to be able to reach DCs of 47 on this server. Also, before the Practised Spellcaster bug was fixed, you could reach DCs of 48...
As for even higher DCs... I think I would go for Druid with splash of Turn Undead class and Hierophant.
Ability score:
20 (Base wisdom)
+ 7 (Ability score increases)
+ 2 (Spellcasting Prodigy)
+ 12 (Owl's Insight)
+ 3 (Great Wisdom feats)
= 44, which gives us the modifier of 17
Caster level:
30 (Practised Spellcaster)
+ 3 (Hierophant Spell Power)
+ 5 (Advanced Divine Spell Power) (You can roll lower, mind you.)
= 38, hence epic spellcaster bonus of +6.
Thus... your DC could be:
10 (Base)
+ 17 (Ability modifier)
+ 9 (Spell level)
+ 3 (Epic Spell Focus)
+ 6 (Epic Spellcaster bonus)
= 45