Let X be a noetherian scheme of finite Krull dimension, having 2 invertible in
its ring of regular functions, an ample family of line bundles, and a global
bound on the virtual mod-2 cohomological dimensions of its residue fields.
We prove that the comparison map from the hermitian K-theory of X to the
homotopy fixed points of K-theory under the natural Z/2-action is a 2-adic
equivalence in general, and an integral equivalence when X has no formally real
residue field.
We also show that the comparison map between the higher Grothendieck-Witt
(hermitian K-) theory of X and its étale version is an isomorphism on homotopy
groups in the same range as for the Quillen-Lichtenbaum conjecture in K-theory.
Applications compute higher Grothendieck-Witt groups of complex algebraic
varieties and rings of 2-integers in number fields, and hence values of
Dedekind zeta-functions.