Pretty straightforward, Im talking mostly about the persuade/intimidate perks.

Once the skill is at 100 are the perks redundant or can you still fail an intimidate?

I'm not sure about intimidate, since it takes your level in account as well. But persuasion always succeeds at 100 speech, or 70 speech if you take the perk.

I have never ran to a situation where I would need a single perk in speech.

Really? Persuade and Intimidate almost never work for me if Im not wearing +speechcraft gear.

Bribes are usually pretty cheap and eventually you start to learn which persuasions are harder than other so you can plan your timing in advance. For example the gate guard in Riften is a very easy persuasion while the Silver-Blood thugs at Kahlwastren (?) are hard to convince.

Right on, its really the Intimidate Im wanting to know about though. I couldnt really find a definite answer.