For sorcerers, do these stack? In other words, if you've got both feats for fireball, you can apply two metamagic feats to the spell, say empower and quicken for no adjustment.
The way I read them, it does.
Spontaneous Metafocus only speeds up the casting time. It doesn't give free metamagic.
An empowered quickened fireball would take up a 5th-level spell slot and be cast as a swift action (with or without Spontaneous Metafocus).
As written Spell Perfection and Spontaneous Metafocus do completely different things, so the question of whether they stack or not becomes moot.
Now if it were an empowered maximized fireball (with Spell Perfection), then it would be cast as a full round action (still using up a 5th-level slot). However, if you had Spontaneous Metafocus as well, then you could cast your empowered maximized fireball as a standard action.
Spell Perfection only makes a single metamagic application free. Applying two metamagic applications to the spell not only ups the spell slot required, but also uses the standard casting times for metamagic'ed spells cast by spontaneous casters (that is, a full round action).