I don't recall seeing a feat like lightning strike anywhere. There is a maneuver from the Tome of Battle that is similar called sapphire nightmare blade. I guess I am prone to the "lean upward' approach. If the only advancement E6 characters get after 6th level are feats, then there should be really awesome feats to work towards. Every feat should feel special. It shouldn't boil down to "Another 5000 exp. Guess I'll take toughness again." I've edited some of my previous suggested feats. I made some of the "lean upward" ones have stiffer prerequisites.
Here are a few more. They may be considered "lean upward" feats.
Precise Strike (General)
Prerequisites: Dex 17+, BAB + 4, Sneak Attack +3d6, Spot 9 ranks, Weapon Finesse
Benefit: Your sneak attack damage increases by +1d6 when wielding a light weapon. You may only take this feat once.
Deadly Strike (Ambush)
Prerequisites: Dex 17 +, BAB +4, Sneak Attack +3d6, Spot 9 ranks, Sleight of Hand 9 ranks, Heal 4 ranks, Weapon Finesse, Weapon Focus, Precise Strike
Benefit: With a successful sneak attack, once per encounter you can forgo 3d6 sneak attack dice on a single attack to deal 2 points of constitution damage to your opponent. You must use a light weapon that you have Wepon Focus for to use this feat.
Arcane Insight (General)
Prerequisites: 18+ in primary arcane spellcasting ability score, Arcane Caster level 6, ability to cast 3rd level arcane spells, Concentration 9 ranks, Knowledge (Arcana) 9 ranks, Spellcraft 9 ranks
Benefit: Once per day you can make a DC 25 spellcraft check to attempt to cast one 4th level sorcer/wizard spell. This takes a full-round action or 2 full rounds if the casting time if the casting time of the spell is normally one full round. Failure means you are stunned for one round. This action counts as casting a spell for the purpose of provoking attacks of opportunity. You may not cast defensively while performing this action.
Divine Inspiration (General)
Prerequisites: 18+ in primary divine spellcasting ability score, Divine Caster level 6, ability to cast 3rd level divine spells, Concentration 9 ranks, Knowledge (Religion) or Knowledge (Nature) 9 ranks, Spellcraft 9 ranks
Benefit: Once per day you can make a DC 25 spellcraft check to attempt to cast one 4th level divine spell normally available to your class. This takes a full-round action or 2 full round actions if the casting time of the spell is normally one full round. Failure means you are stunned for one round. This action counts as casting a spell for the purpose of provoking attacks of opportunity. You may not cast defensively while performing this action.