Top speed, air sensing, and fuel

[NikFu S.]

So I have this purely hypothetical situation, where there is one of those air mass resistors installed onto an SVX, possibly richening the fuel by great amounts.
Let's say everything else is ruled out over the course of a year.

What are the chances this cheap ebay mod, which noone should ever install, is limiting the top speed of this SVX to 125 mph, even causing it to drop the tach to around 4k at that speed?

Does this sound like the fuel pump or something related is put on hyper overtime and is just too tired to push on?