trying to fix my Sonar latency too....
Under Preferences/driver setting I saw the roundtrip latency, then reduced buffers + increased sample rate to 96k....got it down to 9.2ms....ok for mastering I read.
Then took free VOXENGO LATENCY DELAY plugin, set it to reduce 9.2ms....then by ear tweaked it to 9.15....
exported a song....sounds great to me now....will have to hear it back later to be sure.
on a multiple track project, one will have to freeze/bounce tracks, not too much VSTs as most add latency....there are zero latency plugins though....
hope this helps anyone....
greeting & wishing well to US from Europe