Bront said:
Saying he's now faster than other creatures doesn't make it unbalanced, because it's a magical spell.
it is not unbalanced because of being faster than other creatures. It is unbalanced because movement is important part in combat, in combat rules, etc.... and the rules are designed for a specific speed (base speed or enhanced speed)
A base speed chart /per round
5 ft step
10 ft.
15 ft.
20 ft. dwarf
30 ft. human
40 ft. human barbarian
60 ft. fly, expeditious retreat on human
75 ft. human with empowered expedititous retreat spell (wich uses a 3rd level slot and the caster needs a feat)
faster: Dimension door, Teleport, Windwalk
Bront said:
Natural creatures can't cast fireballs, most can't fly, and if they can't be caught by normal means, not a big deal. That's the point of the spell.
Most SRD ground bound creatures have a base speed maximum 60 ft (megaraptor).
The combat rules are based on this movement. With a fly spell a person can catch each land-bound creature.
Bront said:
You mentioned things with a 5' move. Fly and FoF are almost the identical spell here,
A creature with 5´move enhanced by a fly spell has a speed of 60 ft.
A creature with 5´move enhanced by a FoF spell has a speed of 65 ft.
Bront said:
except fly is more powerful by far in this case, because you're not limited to ground movement.
That is correct. But granting more boost to speed is no option to improve the power of a FoF spell to the level of power of a fly spell.
Bront said:
You mentioned 60' vision. Fly takes you out of that range too.
Yes but a creature with fly spell can only fly 60´per round. A full plate dwarf enhanced by a FoF spell can run 80 ft. per round but only sees 60´.
Bront said:
According to the RAW, you can empower an expedious retreat and allow a +45' speed bonus.
That is correct, but
1. empowered expeditious retreat uses a 3rd level spell slot and grants only +45 ft. and not +60 ft.
2. you need a feat for empowering.
3. The range of expeditious retreat is personal
4. If FoF exists nobody would cast an empowered expeditious retreat spell.
Edited: If do not know if you can empower expeditious retreat, because
srd said:
All variable, numeric effects of an empowered spell are increased by one-half.
.
Expeditious retreat grants a fixed +30, a bonus that is not variable.
If you can empower expeditious retreat you can empower the fly spell to 90 ft.
Bront said:
Personaly, I don't think FoF is too powerfull, but just to note than you can already add more than 30' to your movement using spells in the RAW. Not to mention they stack with books of striding and springing, monk speed bonuses, barb speed bonuses, ect.
But you can not add +60 ft ground speed to your base speed using the RAW.

If FoF adds +60 ft:
- it is weaker than the fly spell
- but it is more powerful than an empowered expeditious retreat spell because FoF has a higher bonus and the range is not personal.
Bront said:
I do think that perhaps you should limit the spell to huminoids of medium size or smaller, so no +60' horses.
With your limitation a centaur or giant spellcaster has no benefit from this spell.