If an Eidolon has the Flight evolution, would the Boots of Striding and Springing increase its fly speed?

Question

A summoner's eidolon can gain the Flight evolution, which says the following:

An eidolon grows large wings, like those of a bat, bird, insect, or dragon, gaining the ability to fly. The eidolon gains a fly speed equal to its base speed.

There are many ways to increase a creature's base speed. For example, the eidolon could put on a pair of Boots of Striding and Springing, which increases its land movement:

These boots increase the wearer’s base land speed by 10 feet. In addition to this striding ability (considered an enhancement bonus), these boots allow the wearer to make great leaps. She can jump with a +5 competence bonus on Acrobatics checks.

By default, an eidolon's base land speed depends on its base form (biped, quadruped, serpentine, etc.), and so its default fly speed should equal that amount of movement.

If an eidolon has the flight evolution, and gets an enhancement bonus to its base speed (such as using the Boots of Striding and Springing), will its fly speed also increase? Or does the eidolon's fly speed derive from its unmodified land speed?

Answer 1

I would argue that magic items do not affect a creature’s base speed, only its speed. The eidolon’s flying speed would thus be unchanged by the eidolon wearing boots of striding and springing.

On the other hand, anything that changes the eidolon’s anatomy (and therefore possibly its base speed) would indeed change its flying speed.

Then again, I play Dungeons & Dragons, not Pathfinder, so I’m just translating “base speed” to what it would mean in Dungeons & Dragons.

Answer 2

Strict RAW interpretation: Yes.

Increasing "base land speed" would increase any dependent speeds, unless specified otherwise.

It seems that "base speed", "land speed", and "base land speed" are generally synonymous terms in Pathfinder. The Core Rulebook uses these terms interchangeably.

For example, dwarves have a "base speed of 20 feet" as a racial feature, but the rules about armored movement refer to it as simply "land speed". And later, the the section about movement in combat suggests that the speed in a creature's race entry is the same as its "base land speed":

Your speed while unarmored is your base land speed.

The Pathfinder SRD contains glossary definitions of these different usages of speeds:

Base Speed

Base speed is your unencumbered speed for a specified type of movement. Your base speed for any movement type is calculated in a similar manner as described in Base Land speed. When a speed type is not referenced, base speed usually implies base land speed.

Base Land Speed

Base land speed is your unencumbered speed. Base land speed is calculated by applying all modifiers to your character’s speed with the exception of armor or encumbrance adjustments or any effect that modifies your “normal speed”.

By this definition, if the Flight evolution gives the eidolon a fly speed equal to its "base speed", then its fly speed is equal to its base land speed.

Although the Boots of Striding and Springing mention the spell Longstrider as a crafting prerequisite, the wearer is affected by the item, not the spell. And whereas the spell explicitly says that non-land speeds are unchanged, the boots do not have this limitation. This is unusual but has not been addressed by errata.

Therefore, by RAW, the eidolon's fly speed should include the enhancement bonus from the boots.