Oreo an others, I find your lack of respect for realism worrying. A car bomb is 95% of the time under the drivers seat and is only really designed to kill passengers. If you are expecting to see lots of area damage from from a car bomb you need to think more along the lines of a truck bomb. Something with compressed flammable gas canisters or a dense explosive charges, or if you wish to go down the DIY insurgent / home brew route you need to use a high nitrous content fertilizers and mix it with pure alcohol.
The RPG issue is some what based on real life I am unsure of the top of my head what the exact angle range is but a RPG 6 an 7 can and do a skip as it works on a contact detonator, there are proximity sensors type detonators out there but they are rare not many are available out side of the former soviet block. As for the speed at moving when holding one you are limited considering the MK7 rpg weighs in at 15lb an the normal ordnance can weigh between 3 - 7lb's depending on the explosive an where it was produced and the fact the average bandoleer of 5 rounds and going of the mean weight of 5.5lbs and 5 rounds weighing 27.5lb's adding the weight of the launcher at 15lbs we get a total of 42.5lbs that will slow you down a fair bit. Also it's a large an bulky weapon not a ideal weapon for FUBA fighting even less so when it comes to FISH. But it's also not a super accurate weapon at the best of times it dosn't need to be it was designed to hit a tank or a building not a single person.
I have not played GTA 4 yet an I doubt i will unless one of my friends gets it so i can't comment on gameplay issues, however I will say this GTA has had a good run but it's time it was layed to rest. Back in its day it was ground breaking and caused a stair amongst the hen peckers of the world but it's time it died a dignified death.