Now, of that list, let's focus on Petersen, Patterson and Kelly for a moment...
Chris Petersen - Solid A+ hire if it happens, but you are talking serious dough to sway him from Washington.  However, little to no risk involved in making that hire
Gary Patterson - Another solid A+ hire.  However, he's building a dynasty at TCU and it'd have to be a real solid offer to get him to move.  Like, probably way more than we'd pay.  He's close to that Unicorn level in the coach's world since he hasn't moved from TCU in 20 years.
Chip Kelly - Light risk involved (former NCAA sanctions even though not directly involved), but the man will be coaching somewhere in 2018.  Has already proven himself to be at the elite of CFB rankings.  However, there will be a bidding war by several teams going after him.
All three are not outside the pocketbooks of UT.  However, I'd suspect several colleges have taken a run at Patterson before, Petersen likely as well.  Kelly is waiting on a fat paycheck and can afford to be picky about who courts him.
Now Gruden, the spirit and intent of this thread.
Medium risk involved since the man has been out of coaching for almost a decade.  However, it's not like he's sat on his backside the entire time.  He's learned from watching more football than any of us could possibly fathom.  I'd suspect his playbook is full of all kinds of crazy sorcery and shenanigans that will dumbfound opposing defenses.  And recruiting?  I'd dare say that's a non-issue in the first couple of years.  A name gets you a long way in that world starting off.  But he needs a winning record to back it up.
And paycheck...it's going to be a pretty hefty deal to sway him in.
But overall, he's not the anti-Christ like many screech about on here.  He's a solid hire and while he hasn't proven himself at the CFB level, there is no indication he can't compete at the highest levels if he assembles the right staff.   And furthermore, if UT opened the pocketbook and paid for said decent staff.