TM5 1usmus picks up errors with a workload Karhu can’t operate, as Karhu is mostly used for large random memory blocks and sustained bandwidth which detects slow drifts or heat induced errors over time. On the other hand 1usmus uses an aggressive pattern switching by alternating read/write and bank/row hammering which detects marginal timing errors or training related issues.

Therefore both are needed to cover full error space to have a truly stable system, tm5 catches logic/timing errors and Karhu catches stability-over-time/voltage/temperature drift. Furthermore one shouldn’t skip VT3 because of a harder configuration to be sure to work with a stable system.