Belarusians get north Slavic above 90% regularly at DNA.Land. The only people who get higher North Slavic score that Belarusiansare Lithuanians and Latvians who get 99.9% or 100%. Proxy for North Slavic populations are Lithuanians, Estonians, Belarusians, Russians, Ukrainians, Poles, Erzya, if I am not mistaken. Russians, Poles, Ukrainians get between 60-90%. Western Ukrainians and southern Poles may get as low as 50% . Northern Russians and certain Poles (Mazovians) also get above 90% north Slavic.
Mazovians – ethnographic region around Warsaw, north-eastern Poland next to eastern Prussia – have strikingly similar genetic profile to that of the Belarusians and eastern Lithuanians.
My 23andme results