Drive shaft RPM vs MPH

[THensley]

I have added an Auto Meter 5291 between the speedo cable. I have added a Holley 5in screen with GPS .My Holley HP will convert that signal to RPM or MPH.
What would you choose? Car is a solid 11.5 but I have enough parts to turn the boost up and make it a 10.5 ( I think )
What is best for tuning and logging purpose?

 

[TexasT]

I would do the rpm as the gps should be able to do the mph.

 

[TType85]

I am logging MPH but RPM (drive shaft speed) would be good too, I am using the 12.3 dash I replaced the cable with this 16 Pulse Speedometer Sensor Adapter for GM Vehicles

It is nice to be able to see wheel spin in the logs. I let out right as I felt the spin. I am sure you could do this with RPM just as well if not better.

 

[THensley]

Nice Im running the OE digital dash
I thought RPM might be a little more accurate when I was setting here thinking about it. After I posted and heard from TexesT I started setting up my IOs.
Got to run through the math tonight but I don't think it maters in the long run because the signal remakes 16 per rev.
once you do the speedo gear reduction its 6.5 per rev, if it was directly off the drive shaft at 16 it would be supper accurate.
with all this TEC its easy to over think it.
Im waiting for one more peace of the puzzle before startup.

 

[TType85]

Nice Im running the OE digital dash
I thought RPM might be a little more accurate when I was setting here thinking about it. After I posted and heard from TexesT I started setting up my IOs.
Got to run through the math tonight but I don't think it maters in the long run because the signal remakes 16 per rev.
once you do the speedo gear reduction its 6.5 per rev, if it was directly off the drive shaft at 16 it would be supper accurate.
with all this TEC its easy to over think it.
Im waiting for one more peace of the puzzle before startup.

The closest I could get it to the GPS speed was 6 per rev since it the software won't let you do 6.5 and the signal is a bit rough but that might be my sender or I may need to up the pulses to average.