The less the Nash weight is the less candidates remain after sieving is correct, but also the less chance to find a prime: low Nash = less cand. = less primes.

You could choose a lower k-value which produce smaller test timings for same n-values as 1281979.

Check the Wiki for

low weight k-values to see the difference. You could sieve and test some higher ranges to get a feeling of those.

Looking other tables in the Wiki and sorting by #primes or Nash could help, too.