Since you're nowhere near my timezone I'm going to assume you want me to go on OK?
Part 2: Understanding Performance Files
Open up GPxPatch, click on the GPxSet tab and make sure that the 'Player car performance team dependent' option is set to 'Old behavior'. There's a reason for this but we don't need to cover it here.
Now, in your GP4/gpxpdata folder open up the actual PF file that the GPxSet tab tells you it's using. In my example above it was called somefilename.txt and it looks something like this:
** gp3edit - performance file **
[Team #00]
Name=Ferrari,Ferrari
Performance=758,822,15938
First Driver=1,Alain Prost,15029,540,15412,481
Second Driver=2,Nigel Mansell,15192,456,14726,352
[Team #01]
Name=Tyrrell,Ford
Performance=715,785,23214
First Driver=3,Satoru Nakajima,15686,747,15691,246
Second Driver=4,Jean Alesi,15908,544,16031,390
etc
Let's take a quick look at what each of these values represents:
Performance=(race power, qualifying power, failure probability)
First Driver=1,(Driver Name, race grip, race grip variability, qualifying grip, qualifying variability)
In essence, these values are used to determine the likelihood of mechanical failure for each team and make one driver and/or team quicker than another. The power values are often referred to as BHP values (which they aren't really). Regardless, the higher they are, the faster the cars will go.
You could then, in theory, keep increasing the Q&R power levels of all the cars until you reached your desired speed, but sooner or later you'll run into the gearing problem identified by gap177 above, which we'll be dealing with later. Suffice it to say for now, that the PF is NOT the place to do what YOU want to do. It is simply used to make the drivers and teams perform more realistically, relative to each other.
Thus, in the example above (which is taken from my PF for the first race of the 1990 season) it is clear that the Ferrari cars will be faster and will tend to be more reliable than the Tyrrells, both in qualifying and the race. But notice the grip values assigned to each driver. Clearly the Tyrrells have the advantage in that respect, so we would expect to see Ferraris doing well on the straights and the Tyrrells possibly gaining some ground on the corners. Jean Alesi, in particular, is likely to do well, but chances are the Ferraris will still come out on top most of the time on account of them having 5% (or so) more power.
So what? Well the point is, the PFs should be viewed as something quite subtle. They bring extra flavor to the game, which is why most mods make good use of them. You could just stick with the one PF to cover all the races in a season, but I find it's much more fun to construct a unique one for each race. You see, years ago, a team like Lotus was often known for creating very nimble cars with great handling that weren't necessarily all that fast in a straight line, whereas other teams tended to focus on brute force power at the expense of a bit of handling (like Ferrari or other teams of the period that used heavier V12 engines). Because of this difference, the Lotuses would tend to do well at a circuit like Monaco, which played to their strengths, but the Ferraris would have the advantage at somewhere like Hockenheim where top speed mattered more. The PF is the only place where you can attempt to re-create such nuances in on the track behavior, because the others (MD files, Physics files and Torque files) CANNOT address individual cars or teams directly - only ALL cars equally. This is an important point.
Although I hope to release a very significant update to it one day, PRBlanco's Performance Calculator.xls is an excellent tool for constructing PF files of your own. (I'd link to it for you but I can't find it).
One little tip (in my experience) is to keep the Q&R values between 16200 or so at maximum and 14000 or more at minimum. Set too high the cars might become too easy to handle (like they're on rails), while too low a setting could make the cars which behave like they're on ice, which is frustrating. Fortunately, most mods include a set of PFs, so certainly at first, you can just let them do their thing while you ignore them.
On a side note; some mods make all the power settings the same in the PF - in effect, not using them to regulate power at all. We might touch on the reason for this later, but it's not important right now other than it reinforces the idea that this is not the place to do what you want to do!
My aim here was just to show you where the PFs live and to clarify what you can do with them. For me, they bring GP4 to life.
On another side note: Unlike my example above, I actually store my PFs in a sub-folder called Performance that I create in the gpxpdata folder and I usually include the circuit number in the PF name like I did above. I find it just makes things tidier and easier to work with if ever I need to edit them.
So, if you're OK with the above, we can move on to MDs next and actually get to your question. Let me know how I'm doing so far - and if you have any questions about anything I've covered up to this point, please ask.
PS: I'm trying not to drag this out, but it's just that I'm sure I would have benefited if I could have read all this in one place at the start. I spent... just too long..., sorting all this out for myself and I got totally frustrated and nearly gave up until I began to get some perspective on the way things worked and how they fit together.