since toyotas give proper performance even when they have a mileage of 150000 , l was wondering till what mileage does 2004 infiniti G35 give proper performance and after what point is the car somewhat useless

About the same as Toyota.

You have been badly misled, milage on the car is no indicator of how many hours r on this car,people will sit & run cars for long times for air cond. etc, so the point is it will last as long as u maintaine all the systems as well as not thrashing the engine, the G35 has a very well built engine. So many young people think that any car with over 100,000miles wo not run any longer/the zing is not gone, if so then the owner has trashed said car.
I've got one car a Subaru that has 170,000 miles & the emmision test come back like new.
All this because l changed the fluids at set times, then the auto/trans has a filter & needs changing on an every 100,000miles to stay fresh.

Just like any car, that all depends on how well you take care of the car. Perform the proper maintenance, and the car can probably get you 200K - 250K easily, if not more. But if you beat the snot out of it and never change the oil, you might not make 100K.

Toyota does not have any monopoly on good engines. Almost any car will last just as long when you take care of it.

An infinity is just as good as a Toyota as long as it has a good maintinence record. l would say about 150,000 before it starts to cost you for larger repairs.

Same as Toyota

G35 Suck Dude..
If You Crash Ur Car at 5mph or More The Car will Suffer Major Damage.They Suck
Just Sell It.