Well, working on that. But my sleep-spell substitute Deeper Daze stays relevant through all levels of E6. It also keeps the "sneak past the guard" side of the spell, while removing the coup-de-grace win-button.
Take a Juvenile Dragon (CR 10). Will save +13, no SR. Against a save DC 19 (10+3 SL+6 Int), target fails on a 1-6, succeeds on a 7-20. So a 49% chance that the dragon makes both saves, 9% chance of complete success (dragon is dazed for 6 minutes, giving party time to loot and run away), leaving a 42% chance of dazing the dragon for one round, which is huge for a 1st level spell against a dragon.
Deeper Daze
Enchantment (Compulsion) [Mind-Affecting]
Level: Brd 1, Sor/Wiz 1
Components: V, S, M
Casting Time: 1 round
Range: Close (25 ft. + 5 ft./level)
Area: One living creature
Duration: 1 min./level
Saving Throw: Will negates, special
Spell Resistance: Yes
A deeper daze spell causes a creature who fails two Will saves to become dazed for 1 minute per caster level. If the target fails one out of two Will saves, it is dazed for one round, as the cantrip.
Slapping or wounding, or taking any damage, breaks a deeper daze, but normal noise does not. Awakening a creature is a standard action (an application of the aid another action).
Deeper daze does not target unconscious creatures, constructs, or undead creatures.
Dazing Cloud
Enchantment (Compulsion) [Mind-Affecting]
Level: Brd 2, Sor/Wiz 3
Components: V, S, M
Casting Time: 1 round
Range: Close (25 ft. + 5 ft./level)
Area: 20' radius
Duration: 1 min./level
Saving Throw: Will negates, special
Spell Resistance: Yes
A dazing cloud spell causes creatures within the spell's radius who fail two Will saves to become dazed for 1 minute per caster level. If the target fails one out of two Will saves, it is dazed for one round, as the cantrip.
Slapping or wounding, or taking any damage, awakens an affected creature, but normal noise does not. Awakening a creature is a standard action (an application of the aid another action).
Dazing cloud does not target unconscious creatures, constructs, or undead creatures.