speedo wrong??
 

got my speedo cable replaced and also the cluster and at 50 im at 3000 rpms in 5th, at 70 in 5th gear im at 4000 rpms i dont think thats normal but i cant remember how it used to be. engine is new but stock only thing added is racing exhaust.

tires throw speed off but it will still match speed vs RPMs, replacing a cable won't affect that at all.

The cable is irrelevant but the cluster might be a place to look.
Same series, same transmission option as your original?

your tach could also be off

i never see the tach off, the speedo is based off of the gear on the speedo gear inside the transmission, unless the transmission was changed then it is exactly how it was before changing the cable.

my convertible tach is off by almost 1000rpm at redline, there is even adjustments on the back of the tach

That sounds complete fine for Mazdas...they always have high gear ratios. My MX6 is at 4000 at 120 km/h. I've driven Miatas that are geared super high as well...3000 rpm at 80 km/h this is in 5th by the way.

I suspect that Mazda likes to use mostly underdrive gears for acceleration and i'd guess 3rd or 4th is the direct drive and 5th could just be another underdrive gear. I'm not entirely sure but every Mazda 5 speed i've driven have great acceleration and rev pretty high in 5th gear between 80-120 km/h.