They obviously aren't 55 because NO ONE drives the posted limit.

What is acceptable on the Interstates, etc?

State police usually don't hit under 70. Allegheny County Sherrifs about 65 and local, depending on their mood, 60-65.

As a general rule on highways you'll be good at 65 solo.  Stay with traffic and you won't have a problem. That's usually up to about 80.

Most areas are pretty lenient on the zones that are still 55. Hell, the turnpike just went up to 70 and now everyone averages 75 -- myself included.

Keep it under 80, no worries.

The Route 22 corridor got some kind of additional funding last year for some additional attention but I believe it was only for a few months (and it showed).  My old commute used to take me through the city and parkway west and Route 19.  It was hard to get to the speed limit let alone over it but on Route 79 in the morning there was no speed limit unless a cop was driving by and that's who set the pace...at what seemed like 80 MPH in a 55 zone.  They must have gotten yelled at because eventually the cops were driving right at the speed limit with everyone slowing down and backing up behind them.

On the parkway east if the state police are out there it seems like 20 MPH over is when they want to pull out and get you.  Route 22 in Murrysville, can't say but they are quite active with speeders on their little section of 22.  Further east the PA state police like to hang out where the speed limit goes from 55 MPH to 45 MPH.  Most people are doing 65 MPH and the short section, like 3/4 of a mile that it is 45 MPH is when they strike as you are now 20 MPH over.

376, usually 70mph if lone wolf, and up to 80mph in a group.

As far as the locals go, it varies and some do use certain roads for revenue generation.  I only know of a few, not close to canonsburg, even though that is one of the places I work near.
FReedom Road in Beaver Country is one of such road.  Posted 40.