I had this issue in my 94, and improved the situation by changing the radiator, and crossover pipe..
Most first gen Marks (but not all) have this issue, where the temp gauge moves in real time. My 95 Taurus was like that too.. Basically there is a large range of temps that "Normal" covers.. I have a 99 Accord, and whether its running at 185 or 205, its sitting pretty much dead in the middle. My Lexus 08 SC430 I just got, is the same way, and will sit in the center no matter how hot out it is, no matter how much i blast the AC, and no matter how steep a hill I take it up, although I never checked it on this car. My MN12 Tbird sat right in the middle between 170 and 195.
One day my Mark was running warm and started to ping when going uphill in the canyons in Hollywood, and it was about 105 out.. The temp gauge was at the N, literally just before overheating (stupid design), but when I checked the coolant temp with my temp gun it was 207 degrees. My Mark always did run a little warm, but I think there were some other issues which is why I got rid of it.. Racebronco came to pick it up! My Taurus always ran in the upper normal range, but when the AC was on, it dropped below middle, and it did this whether it was hot or cold out. I checked the temp on this Taurus since its the same idea as the Mark, and it was barely 195 when it was in the upper normal range.
Apparently, a lot of Ford dealers had to deal with seriously pissed off people who just dropped $40-$50k on a premium car, but thought they were overheating! This caused a lot of owners to disregard the temp gauge, and then blew their engines later on after owning for a while, because they did not know it was overheating.
I am going to play around with my Lexus a bit (turned out to be a freaking awesome car), but will get another Mark in the next couple years, a second gen LSC with no more than 100k miles.. Its supposed to go 0-60 in about 5.6-5.7 seconds with the 6 speed, but my Mark still felt a good deal quicker even though its about a second slower to 60, and was able to spin the tires so easily, while this SC wont spin much unless you brake torque it. This Lexus and the Mark are both 3800 lbs, and have pretty much the same power but the Cobra engine is more wild when you push it.. If the Mark had a sophisticated trans like my glorified Toyota, I'm pretty sure it would even be faster.
One of the best things you can do for a first gen Mark is to get an aftermarket temp gauge... Assuming your cooling system works perfectly, you would be surprised the temp reading off the coolant, versus what shows up on the temp gauge. Of course the second gen Marks, usually sit right in the center, and of course you are also able to get a temp reading directly from the VMM so that helps as well!
Also get an external trans cooler if you are in warm climate and bypass the one in your radiator. The external trans cooler works better and protects your trans better while adding fluid capacity to the system, and allows you radiator and fan to only work on cooling your engine - It DOES make a nice difference