Context here, from 4:40 to 4:46.
Scaling[]
Shepard's head = 268 pixels (White Line)
Panel's height = 1077 pixels (Black Line)
Calculation[]
Shepard's height = 188 cm
Human head's average ratio is between 1 to 6.5 and 1 to 8.
Shepard's head = 188/8 = 23.5 cm or 0.235 m
2*atan(268/1077/0.7) = 0.683105371 rad or 39.1390547 degree
http://www.1728.org/angsize.htm
Distance between Shepard and Gavin Archer = 0.33053 m
Mass accelerator weaponry are supposed to fire bullets at relativistic speed, but since i don't know how exactly fast i will assume various ends.
Low End = 10% SoL = 299792458*10% = 29979245.8 m/s
Mid End = 25% SoL = 299792458*25% = 74948114.5 m/s
High End = 50% SoL = 299792458*50% = 149896229 m/s
Based on this scan Shepard seen to have perform a 75 degree movement with his upper body.
75 degree = 0.208333 turn
Average torso for human male is between 46cm (18") to 52cm (20.5"), i will then assume that Shepard is in the middle.
Shepard's upper body = 49 cm or 0.49 m
Movement = 0.208333*(2*0.49*pi) = 0.641407474 m
LE Timeframe = 0.33053/29979245.8 = 1.1025294e-8 seconds
ME Timeframe = 0.33053/74948114.5 = 4.41011762e-9 seconds
HE Timeframe = 0.33053/149896229 = 2.20505881e-9 seconds
LE Speed = 0.641407474/1.1025294e-8 = 58175997.3 m/s or 0.194054239c
ME Speed = 0.641407474/4.41011762e-9 = 145439993 m/s or 0.485135595c
HE Speed = 0.641407474/2.20505881e-9 = 290879985 m/s or 0.97027119c
Result[]
LE = 19.405% SoL (Relativistic) [ACCEPTED]
ME = 48.514% SoL (Relativistic)
HE = 97.03% SoL (Relativistic+)