In chapter 447 of Fairy Tail, Laxus intercepts a sand wave made by Ajeel. I'll be calculating the speed required to perform this feat.
First, I'm gonna need the height of Lucy's head. You'll see why in a bit. To do this, I'll be borrowing measurements taken from here. This first bit of pixel scaling comes from there, except now with 1.75 meters as Natsu's height since we use that nowadays.
Natsu's Height = 1.75 meters = 300 px
1.75 / 300 = 0.00583 meters per px
Lucy's Height = 288 px = 1.68 meters
A human's head is 13% of their body, so with that...
Lucy's Head Height = 1.68 * 0.13 = 0.218 meters
Now for some more pixel scaling.
Top Right Panel:
Lucy's Head Height = 0.218 meters = 35.85 px
0.218 / 35.85 = 0.00608 meters per px
Makarov's Hand Width = 202.24 px = 1.23 meters
Top Left Panel:
Makarov's Hand Width = 1.23 meters = 63.69 px
1.23 / 63.69 = 0.01931 meters per px
Makarov's Height = 258 px = 4.98 meters
As for the sand wave itself, as shown here, it comes from the horizon. Not only that, but excluding cinematic time, the timeframe is 2 seconds. The cinematic time is Ajeel talking with the dark background, as in the manga, he's talking while the sand already crossed the distance. So, our timeframe is 2 seconds with 20000 meters for horizon distance.
Sand Wave Speed = 20000 / 2 = 10000 m/s
Makarov's Height = 4.98 meters = 19 px
4.98 / 19 = 0.26211 meters per px
Distance from Sand Wave to Makarov = 3 px = 0.79 meters
Time = Distance / Speed = 0.79 / 10000 = 0.000079 seconds
As shown here, Laxus' lightning was cloud to ground. Low-end of this is 1000 meters and high-end is 15000 meters, so I'll use an average of 8000 meters as the distance traveled.
Laxus' Speed = 8000 / 0.000079 = 101265822.79 m/s
Laxus Intercepts a Sand Wave = 101265822.79 m/s; 0.34c (Relativistic)
Again I say, oh my god.