EQG Geode Rainbow Dash Speed Upgrade
She built an entire set, ran to Applejac's house while building and back, and read her diary in about 9 seconds.
https://www.youtube.com/watch?v=6EkDwcRukfs
Pinkie Pie destroys a section of log the size of a short bus.
https://www.youtube.com/watch?v=1k1_ggLTph4
[1]
According to the above image, the farm lies outside of the city. While this map isn't exactly to scale, we can still use it as reference.
According to wikipedia, the smallest major city in the US has an area of 196 km^2. Could Canterlot be larger? I'm not sure. If this was arranged as a circle, the radius would be about 7.9 km. Half is 3.95 km. Double these distances because she ran to the farm and back.
15800m and 7900m
Since he built an entire set, ran to Applejac's house while building and back, and read her diary in about 9 seconds, we can estimate the travel time to the farm be at most 5 seconds, possibly lower.
15800m / 1s = 15800 m/s = Mach 46.06
7900m / 1s = 7900 m/s = Mach 23.03
15800m / 2s = 7900 m/s = Mach 23.03
7900m / 2s = 3950 m/s = Mach 11.51
15800m / 3s = 5266.66 m/s = Mach 15.35
7900m / 3s = 2633.33 m/s = Mach 7.67
15800m / 4s = 3950 m/s = Mach 11.51
7900m / 4s = 1975 m/s = Mach 5.7
15800m / 5s = 3160 m/s = Mach 9.21
7900m / 5s = 1580 m/s = Mach 4.06
Supersonic+ (Mach 2.5-5): 1
Hypersonic (Mach 5-10): 3
Hypersonic+ (Mach 10-25): 5
High Hypersonic (Mach 25-50): 1
The mode appears to be
Hypersonic+