Re: Summoning
The Summon Monster spells (I-IX) are unchanged in all regards - after all, they only last a matter of rounds and essentially they're not much use for anything beyond combat.
The Planar Binding Spells are a different story entirely, however. These are employed for more complex tasks - either with the use of a Magic Circle (if you're in a desperate hurry) or with a thaumaturgic diagram (if you're taking the correct, sensible precautions). This gives much more of a ritual magick feel- after all, it takes 3 hours to inscribe a diagram if you "take 20."
And consider - the most powerful Summoning Spell (IX), allows you to bring, say, an Astral Deva or a Night Hag. It will serve you unfailingly for a minute or two. This is small potatoes.
Planar Binding can, in theory bring a Balor, Pit Fiend or Death Slaad. Greater Planar Binding: a Solar (it has a 24HD cap). Of course, it's risky, but an unpalatable deal to Mostin (who is good-ish in alignment) is going to be no problem for a CE summoner who is happy to sacrifice virgins in order to slake a demon's thirst.
And Greater Planar Binding is an *8th* level spell.
It is reasonable to assume that a 9th level analog can be extended to include very powerful demons (Lords, maybe Princes) and devils (Dukes of Hell).
Not that Mostin can cast 9th level spells.
Yet.