HSTVL is 2x faster to 50KPH.
18.6% more top speed.
22% more pen.
2S38 has 82.16% of the pen of HSTVL.
84.34% of the top speed.
Some examples of light tanks with similar or more similarities than those two:
AMX-13-90:
7.7, 61kph top speed, 18.6hp/t, non-stabilized, 320mm penning HEATFS round. Reloads fastest among these.
Ru-251:
7.3, 80kph top speed, 25.9hp/t, non-stab, 320mm penning HEATFS round.
C13 T90:
7.0, 70kph top speed, 25.2hp/t, non-stabilized, 250mm penning HEATFS round.
T92:
7.0, 57kph top speed, 20.12hp/t, non-stab, 254mm penning HEATFS round.
leKPz M41:
6.7, 72kph top speed, 21.64hp/t, non-stab, 254mm penning HEATFS round.
Pbv 501:
6.7, 65kph top speed, 25.07hp/t, non-stab, 300mm penning HEATFS round.
Type 62:
6.7, 60kph top speed, 20.48hp/t, non-stab, 300mm penning HEATFS round.
Type 63:
6.3, 64kph top speed, 21.65hp/t, non-stab, 300mm penning HEATFS round.
Yeah, my belief that HSTVL is 1.0 stronger than 2S38 stands on its own without looking at those light tanks; those light tanks however make my belief stronger.
And AMX-13-90 is a good light tank at 7.7, not over-BR’d.
Definitely getting the Ru 251 for my 7.7 German lineup next sale.