What is the diff btween a reg. track and pursuit frame? Also is one more comfortable for street riding? Is one more durable? Lighter?

a tt/pursuit frame might have a lower bb, slacker headtube and steeper seatube.

A more general purpose track frame is better for riding on the street in pretty much any situation but a road frame will probably be better then either for many.

Neither are suitable for street riding.

I disagree, many people ride track bikes on the street.

suitable is a relative term... neither are DESIGNED for street riding, doesn't mean they can't be riden on the streets and function just fine.

Depends the kind of parts you throw on it. I've seen alot of pursuit track frames online with crazy sloping top tubes and pretty much totally inappropriate street geoemtry, but they made up for with riser bars. People can get away with deep drop bars on regular track frames because you just keep your hands next to the stem.

Simple answer, track frame.

You can bet your ass that thing isn't made for the street but I'd ride the s*** out of it through downtown.

$0.02

Doesn't mean they were designed to be used on the street. For gods sake why do we even have road bikes in that case.

just get custom frames built for how you want to ride.
ride the hell out of them.
ignore the human tendency toward semantic battles of genrefication.

i ride a track bike on the street... it's much more comfortable to ride than a roadframe conversion on the street. higher bb, tighter geometery, etc.
ride what you ride.

I agree with that. You'd think a road frame would be more comfortable on the road, but I find my track frame to be more comfy than any of my road frames, even for long distances, unless the roads are rough, then my track bike kills me.

I have ridden both Pursuit frames (radical slope and standard design) and Sprint frames extensively on the street. All the sprint bikes I have had (Coppi x 2, Gardin and Rossin) were all steel and very tight geometry wise. Both Coppi's and the Rossin were standard design and had lots of toe overlap and usually around 75 degree H.T. with shorter proportionate top tubes. The Gardin was a severely sloping bike and was terrible on the street. All these bikes were super tight and had a reatively harsh ride for steel owing to how steep and short they were.
The Pursuit style frames I have had (Rossin, G.T. and Winterbourne) all had a more relaxed ride. Both the G.T. (Easton) and Rossin (Dedaccai Aero) were super stiff at the B.B. frames but were much smoother riding on the street. Mostly because the top tubes and front center dimensions were longer. still have a steep H.T. angle but because of the longer top tube, no toe overlap, even with my size 12 canoes and XL toe clips. When I purchased the Winterbourne Custom (Mostly True Temper OX, Columbus stays)I wanted a more T.T. style bike as I find the longer cockpit and lack of any toe overlap friendlier and more comfy for the street.
They are all track bikes. Not a single one has/had a brake hole. They all saw track use and performed fine. Some were better street bikes than others. None had a noticeably shorter lifespan then any of the road or hardtail mtb frames I have put through the same amount of abuse.
Bikes are bikes. The only limitation is how hard you are willing to ride them and the care you put into taking care of them. My $1 and 2 cents.

oh, and you never see mtn bikes and downhill bikes riding down the sidewalk.

I've never seen downhill bikes riding down the sidewalk (not any serious ones, anyways), but your point is correct. If it's got two wheels, you can ride it in a city and do fine.