Was GTA4 really a bad port, really, or are people all to happy to throw around the term "bad port", and unoptimised around without thinking for any game that runs slowly.
It ran like utter turd on the 360, it was slow, going over bridges at night was painful, truly painful on my eyes it would go so slow. IT ran better on my PC at far higher settings than on the 360.
It was just a bad engine, like others before it, it massively massively overused certain lighting effects which pretty much sucked all the power out of the hardware. Frankly it was just a bad engine that used to much power on some very poor overall effects, leaving little power for other things.
A bad port, to me, would be a game that ran fantastically on a console, but ran like utter crap on a PC. A bad engine, or poor choices in the engine, would give you a game that ran slowly on the console and slowly but still better on a PC at vastly higher settings.
PC's are more powerful you can generally expect to have faster framerates with a decent card at 1920x1200 with full af, decent AA over standard settings on the console at lower res. This was achieved with GTA4, just because it was still poo, it was still better.
It wasn't the bestest port ever, it certainly isn't close to the worst, as I said, bad would be running similar framerates at similar settings/res, which isn't what happened.
As for GTA 5, I would expect it to look better and be a better made engine, with better choices made regarding where to spend the power available. I can't imagine it could run badly on the PC because GTA 5 will have to fit into the available ps3/360's existing power, PC's will have moved on yet again, we'll be on 6870's with uber cheap 5870's by the time its released.