i ran the new cams in with job gibbs BR30 which is 5W30
the new cams and valves sound super quite. i have to really get my ear down on the engine to hear some mechanical noise.

do i replace the oil now and what's best oil for super quite valve trainn

What engine?

Indeed...

what engine?
what tune?
what oil does the engine manufacturer recommend?

full rebuild 1600cc 16v AFH on schrick 264 mild cam and cb600 bike carbs.

Nothing about that build spec suggests it needs anything other than a good quality oil in the manufacturers recommended grade.

Opie Oils suggest 10w-40 semi with regular changes is fine, as an upgrade 5w-30 or 5w-40 synthetic.