Don Durito
Hero
As I said earlier, the main cause of lingering injuries is being reduced to 0 hit points, not massive damage. The other effects of System Shock still apply.I think solely having lingering injuries on mass damage would make it almost unheard of past level 5 where most combat characters will need to suffer 25+ damage. Even with crits that seems rare to me.
I may well keep it to a straight up Con save to avoid the crit effect. With failure resulting in a minor effect and a failure by 5 resulting in a longer save. DC being half the damage taken. Most fighters will pass a DC 10 save without too much difficulty and plenty of other classes too. Particularly with the many bonuses characters can get to saves. That keeps it real, gives them a reasonable chance of avoiding them but makes failure a common enough possibility.
I drop the Con save to save time. Instead System Shock is D20 plus lowest of Con or Str with a 1 always being a 1. This means there is a good chance of system shock doing nothing (as the entries only go up to 10) and as Con contributes to that roll there is no need for an additional roll - (And Str actually matters for once in a situation where it should). Lingerining injuries only happen on a total of five or less. The threat is really enough.
Another reason to keep it for massive damage is that creatures with multi-attacks will not dramatically increase the chance of a lingering injury.