This is probably a stupid question but if a larger diameter turbine is putting out the same thrust as a smaller turbine but at a significantly lower rpm, is there a difference in performance? For example, a P-70 at 3.7" diameter needs 123,000 rpm to produce 17.5 lbs of thrust but a 4.4" P-120 needs only 105,000 rpm. Seems like the smaller turbine would have to put the air out faster to achieve the same thrust.

I've never heard mention of "exhaust gas speed" but if it's different does it affect performance (such as with prop pitch, length and rpm)? Would a same thrust, higher rpm turbine fly faster than a lower rpm one? I'm guessing not in a practical way but it's still an interesting question.

Any thoughts?

Craig