joe603 wrote:care to elaborate? ....maybe say more than two words??
I am not sure how much you actually know about the mechanics of cars, but the statement that clutch fluid gets as hot as brake fluid makes no sense.
It doesnt. Brake fluid gets hot because the fluid runs into the brake calipers. When a vehicle is braking the energy of the vehicle is being converted to thermal energy at the contact point of the brake pads and rotors. In other words, heat transfer is what stops a car. The more you brake, or harder you try to stop the hotter the brake componants get.
The clutch fluid system works nothing like the brake system. The clutch componants and flywheel are somewhat hot when somebody rides the clutch and causes undo friction. Also those componants are slightly warm already because they are bolted to the crank. However the fluid never touches the clutch or flywheel. The closest the fluid gets to the clutch is the outside of the bellhousing, and on a RWD car the inside of the bellhousing is hollow. The transmission will get warms because it is always moving, but it doesnt touch the slave cylinder or the fluid on a G35.
The path of heat transfer from the clutch to the fluid is this: Pressure plate, release bearing, release bearing sleave, clutch fork/lever, push rod in slave cylinder, then to the fluid. So the heat has to travel through a bearing, a thin piece of metal (fork), and an 1/8th inch push rod before it reaches any fluid. Not to mention the slave cylinder is located outside the transmission so it is cooled by the air. How does this manage to equal near boiling brake fluid? Granted I will give you that the clutch fluid piping does run through the engine bay, but that means it will only soak some of the heat given off by the engine, and while it is hot under the hood, its not that hot.
Therefore shifting regardless of RPM, the fluid shouldnt be any hotter or cooler except for the heat the engine is making under the hood at those temps. I cannot explain your pedal problems, but I have been around plenty of cars that do not have the problem you reported.
Onto fluids. The bottom line here is that Nissan/Infiniti says that DOT3 is fine. Its not like 4 is somehow greatly superior to 4, 4 just has a higher boiling point. Higher boiling points are great and all, but 99% of drivers never heat up their brakes enough on the street to warrant the temps the 4 can provide for.
Fluid is fluid, it cannot help stop a car in a shorter distance because of its higher boiling properties, unless you are comparing stopping when fluid is cold vs stopping with overheated fluid. You are trying to stop a vehicle of a given weight. The BEST way to make a car stop in shorter distances is to drop its weight. Other factors such as upgraded brakes, better tires, properly inflated tires, and ambiant condition will help stop in shorter distances. The higher boiling temps help when you are looking for performance on the track because the fluid will hold its properties better, longer. I am not sure how it would help in panic stops, unless you are doing multiple panic stops in a row, thus heating up the brakes.
DOT 5 and 5.1 are options, but there are other things to take into consideration. Water and contaminants cause lower boiling temps. Since DOT3 and 4 are at least a small percent water they are capable of absorbing it a little better than 5 which just isolates the fluid. This causes corrosion issues inside the lines. DOT5 can also break down greases and cause other problems in the system, these become contaminants and obviously lower boiling temps. One other thing to consider is that once you add silicone based 5, you will never fully remove it from your system if you switch back to 3 or 4.
Now just for reference I use ATE Super Blue Racing Fluid (DOT4), in my 240SX. Its blue which makes proper bleeding of the system easy. Bleed the fluid, you know you've bled the system once the fluid goes from yellowisg orange to blue.
*I did not proofread this after typing...
Sorry I had to do that. Seriously you right. It is harder to read when all the letters are capital. 
