I am seeing top speeds in Sport mode of 60's and 70's MPH (with a backwind), can this be right or is the Go 4 app measuring in Kph and listing it as MPH?

yes, it's a fail

good way to answer your last question: next flight, set units to imperial, fly in one direction, record max speed, switch to metric (km), fly in the same direction and record max speed. if they both read the same number followed by mph or kph (depending on the unit selected at the time) you know one of them is wrong.

The top speed of a P4 is 45 mph in sports mode, but that's in dead calm.  So if you add the tail wind, you can see it's possible to achieve very high ground speeds.  If you add gusts, you'll go even faster.  
Here's a great site to check on wind speeds and gusts at elevated heights in your area:  www.windytv.com

I was doing a range test yesterday on my P4 and was flying over a river from bridge to bridge which are approx. 3km distance apart. On the way back (in sports mode) i reached 76km/h according to the flight logs. I didn't realise the thing could fly that quick!

Sorry, slightly off topic.

Mark The Droner Posted at 2017-2-1 14:42
The top speed of a P4 is 45 mph in sports mode, but that's in dead calm.  So if you add the tail wind, you can see it's possible to achieve very high ground speeds.  If you add gusts, you'll go even faster.  
Here's a great site to check on wind speeds and gusts at elevated heights in your area:  www.windytv.com

Thanks, for this it is actually accurate, dont use uavforecast.

You wouldn't be launching the Phantom if there was a strong enough wind to push it that fast and if you did, you wouldn't get the Phantom back.

The_Death_Angel Posted at 2017-2-1 15:35
I was doing a range test yesterday on my P4 and was flying over a river from bridge to bridge which are approx. 3km distance apart. On the way back (in sports mode) i reached 76km/h according to the flight logs. I didn't realise the thing could fly that quick!

Sorry, slightly off topic.

That's about right 76kph in sports is top speed,

Yes it's a bug dji are aware so should be sorted in upcoming soft wear..

KevDrones Posted at 2017-2-1 15:51
Thanks, for this it is actually accurate, dont use uavforecast.

Yeah the windytv is a bit of a learning curve but it's worth it.  I check the GFS and the Euro at 330 ft, and then I look at uavforecast at 450 ft and then I avg everything out.  The nam only gives surface winds.  Then before I head out directly into a strong wind, I set the gimbal to FPV mode so the camera will tilt with the AC and I can then tell if the forecasted wind direction is correct or if I have to adjust a little.  Then when I finally get out far enough and turn around, I know exactly what direction the wind is blowing before I slam it into ATTI for the quick ride home.

Yes its KPH not MPH. Silly bug. You can double check another way also: open your flight log in DJI Go 4 amd scroll thrpugh your flight. I found that even though the app imcorrectly shows KPH when flying, the flight log review in the app properly converts to MPH when reviewing.

KevDrones Posted at 2017-2-1 15:51
Thanks, for this it is actually accurate, dont use uavforecast.

To get wind speeds at various altitudes in uavforecast, you need to go into the settings and set the desired altitude.   It will be fairly accurate for the desired height.

with my p3a I sometimes see 41 mph

What is FPV mode and the other mode mean?