Driving is better with the controller purely because with a keyboard you only have an on/off state. So you only have one level of acceleration, one turning speed.
With a controller, you can slowly pull away (and on GTA V currently on consoles, it even makes the controller rumble a little, simulating the clutch biting point). And in some of the higher-end cars it is very important to not pull away at max throttle as you'll just spin the tail out.
You can also make slow turns, and it just feels more natural.
Yep, controller is so much better for this.
GTA V gets around the issue of aiming from the window by having a 'slo-mo' button.
Though I think that might just be one specific character (can't remember)
The cars handled slightly more 'realistic' in GTA IV IMO, but you get used to GTA V quickly and the controls in general are just so much better than GTA IV. Shooting, taking cover etc is much more fun.
With regard to GTA IV, I recently installed it and ran FRAPS on the following settings:
1080p
Texture Quality: High
Reflection Resolution: Very High
Water Quality: Very High
Shadow Quality: High
Night Shadows: High
Texture Filter Quality: Antisotropic x16
View Distance: 100
Detail Distance: 100
Vehicle Density: 21
Definition: On
V-sync: Off
And the most I got was 39fps on the following spec:
Intel i7 4770k @ 4.5Ghz
8GB Ram
AMD R9 290x 4GB
Samsung Evo SSD
Windows 8.1
I played about with all the settings, and the only one that seemed to (slightly) affect the framerate was the shadows. Even on very low it only pushed it up to about 45fps though.
I've seen people with lower specs say it runs great at 60fps+ though?!
Also tried at 1440p and that lowered the framerate to 33fps.