OK this is for the 88 300E but it may apply to your car, too. I took the resistor out of mine and test drove the car. I noticed NO difference in performance.
I went back home and hooked up my timing gun. With or without the resistor plugged in, there was NO difference in the initial (idle) timing. In both cases my timing was about 8 degrees.
I put back the resistor closed the hood and forgot the whole thing.
However, the idea had really gotten into me and latter on in the evening I decided to spend some time taking timing measurements at other rpm, too.
I had a few more resistors handy and decided to test them all.

First thing, i tried all the resistors (as well as no resistor at all) and measured the timing at idle. In all cases, the timing was 8 degrees. So, these resistors DO NOT change the initial timing.

I repeated the process, this time at 3200 rpm with the vaccum connected to the EZL. Again, the timing did NOT change, and remained constant at 41 degrees. So, the resistors DO NOT change the timing at higher rpm under high vacuum conditions, either.

Third time, I disconnected the vacuum from the EZL and repeated the process checking the timing obtained at 3200 rpm with every different resistor including no resistor at all. Here is what I got:

Stock resistor (470 Ohm): 27 degrees
250 Ohm resistor: 20 degrees
2,000 Ohm resistor: 23 degrees
1,000 Ohm resistor: 27 degrees
No resistor: 27 degrees

I was as surpised as you probably are and repeated the whole process to double check my results. Again, the results were the same.

Lesson learned: First, the stock resistor (470 Ohm) gives the highest timing value. Second, changing this resistor only affects the timing under low vacuum conditions, in other words only when you step hard on the gas pedal. All the other times the timing is not affected by this resistor.

So, I put back the stock resistor verifying for one more time what I always knew. Do not mess with what the factory engineers have done, the stock setup is as good as it could get for the purpose of the car.