I would find it hard to imagine these things getting up past your estimated 130-140 mph. If we had some numbers for your speed ramp (say from 70-110 mph) it could be a little bit easier to guess how much more "go" is left, but regardless, I just don't think there's enough power to overcome the drag nearing the 130mph mark.

Edit**

For reference I wanted to compare some numbers to my old 1993 4cyl Toyota Camry I had that I remember topping out somewhere between 120-130mph (not speed limited.. .just ran out of juice).

Here is what it looks like..

4runner power to weight ratio is slightly higher, at .0442 vs the Camry at .0425, but the coefficient of drag is increased, .36 for the 4runner vs .28 for the Camry. Just using that as a base for comparison.. I stand by estimate of 130 for the 4runner lol.