I recently asked Andrew Low, the man behind LOW// Bicycles what makes the new sscrit model special for fixed criterium racing. This is what Andrew had to say:
"The ss crit is designed to be stiffer than the track bike (track std). This is achieved by using a large, round downtube, which resists torsion and bottom bracket deflection, but some aerodynamics are sacrificed. In a crowded group race on a closed course, aerodynamics are not as crucial as on the track or in a time trial, but the increased stiffness is beneficial for constant acceleration/deceleration.
The Track Std. is designed more with aerodynamics in mind. This is more beneficial on the track where speed tends to be more constant, and where you won't always be protected from the wind by other riders. For this frame we use a downtube with a more aerodynamic profile.
Bottom Bracket Drop:
Both bikes are very responsive and have similar handling characteristics (both bikes can be used just fine in a crit or on the track), but the ss crit is designed to have a slightly higher bottom bracket to give it a bit more manoeuvrability than your average track bike. This is beneficial in a race that is more chaotic than track racing. Also, the higher bottom bracket makes it less likely that your pedal will strike the ground on a tight, flat turn."