As a general rule, Practiced Spellcaster applies where it's most beneficial... so in this case, it applies before Spell Power, and stacks.
You left out one possibility - 19 for all spells except Enchantment, 20 for Enchantment. This is what you get if you apply Practiced Spellcaster after Spell Power (since Practiced Spellcaster cannot raise caster level above your hit dice).
Your right I did too......That's what I was thinking as well. Makes the wiz10/min10 look prety nice doesn't it? Casts up to 8th level spells, Casts them at lvl 19 unless there enchantment and there cast at lvl 23.....Very nice indeed.