In a 3.0 set up with the correct Diff, both the Manual (3.7) and the Auto (3.9) will run around the 2625 to 2650 RPM mark at 70MPH allowing for some Speedo error, your probably find your 70MPH is actually around 67/68 in true speed as the speedo's tend to read high, even on the Ex Police with Calibrated Speedo's they run around the same RPM at a tue speed of 70.
What I can tell you is if you run a Manual set up with a Auto diff (3.9) on the 3.0 setups you be doing around 3000RPm at 70, which is a tad anoying on a Motorway Cruise IMHO.
I cant remember now if the 2.5 (never owned one) had the same 5th gear ratio as the 3.0's, seem to remember hearing the very early ones were and the later prior to going to 2.6 were slightly different.
Here you go, just checked my hand written Notes from a few years back -
PFL 1994 to 1997/8
2.5 Manual 5th Gear Ratio 0.85 Diff 3.7
3.0 Manual 5th Gear Ratio 0.81 Diff 3.7
MFL 1997 to 2000
2.5 Manual 5th Gear Ratio 0.85 Diff 3.7
3.0 Manual 5th Gear Ratio 0.81 Diff 3.7
FL 1999 to 2000/1
2.5 Manual 5th Gear Ratio 0.85 Diff 3.9
3.0 Manual 5th Gear Ratio 0.81 Diff 3.7
FL 2000 to 2003
2.6 Manual 5th Gear Ratio 0.85 Diff 3.9
3.2 Manual 5th Gear Ratio 0.81 Diff 3.7