Horn of Gorgon allows a better ratio of inherent Str on the 3rd casting.
You should cite your source, specially when it comes to optional Material Components which no one has ever indexed before.
Horn of Gorgon + a Fell Energy Wish lets you do it on the first casting if you're Undead at the time.
Not really.
For reference,
Horn of Gorgon: Gorgon horns soften when soaked in a particular kind of rare vinegar. If this horn of gorgon is then used as a component in the casting of any spell that enhances Strength—whether by an enhancement bonus, a size increase, or any other means—it adds 2 to the subject's Strength, on top of the spell's normal effects. Price: 575 gp.
The horn actually adds it's own bonus to Strength that's applied on top of the Spell's effect rather than directly increasing the bonus the Spell provides.
So on the one hand you cannot benefit from the Horn's effect more than once due to stacking rules but on the other hand you keep the benefit for as long as the Spell's effect lasts. So technically you still need Wishx3 with Fell Energy on last one will take you to the cap on inherent bonuses. It just happens to be using the Horn an something that will provide a permanent effect is a very good idea.
And truthfully, Strength is by far the easiest score to raise up. You can actually pick up a +4 inherent bonus for 40k using one of the Undead Arms. You save 70,000gp with no downsides (like fiendish ones make you save vs evil or elemental decreases hp). Then I think it's Defenders of Faith that offers the Arm of Nyr which gives a +2 unnamed bonus to Str & Dex and +2 Deflection to AC for 12k. With just those two things you'll exceed the +5 undispellable gain a Tome provides and save money doing it.
And when you get into Spells, Bite of the Werebear gives a +16 Enhancement Bonus & Giant Size offers a +32
technically unnamed but size effects don't stack anyway and both are 7th level Persistable effects. Convince a Wu Gen to help make a Staff with you and just use a Minor Schema of Metamagic Item to apply Persist to it for 25 days of +48 Str for 125,437.5gp which is
still less than the price of a +5 Tome.
Pretty much if you track inherent bonuses on your WBL (like you probably should) they just plain are too expensive to waste time buying Tomes or casting Wish.