Comparison shows the cause is in CSIT code, +20 to +30% depending on test case.

The VPP2001+CSIT2001 results give high stdev, making it hard for bisect to find the cause.
Using CSIT2005 code (with either VPP) shows smaller stdev, especially for l2xc as vswitch.
This is true for 2n-skx and 2n-clx, but 3n-hsw has non-negligible stdev also with CSIT2005.