A perturbative new family of fermions is now severely constrained, though not
excluded yet. We reconsider the current bounds (i.e., direct and from Higgs
searches, R_b, oblique parameters) on the fourth generation parameter space
assuming the case of a small CKM mixing with the third generation. We identify
viable scenarios featuring either a light or a heavy Higgs boson. A set of
representative benchmark points targeted for LHC searches is proposed with a
normal (inverted) quark mass hierarchy where t' -> b'W (b' -> tW) decays are
sizable. In the case where the fourth generation couplings to the lighter quark
families are small, we suggest that search strategies at the LHC should include
both pair (strong) and single (weak) production with bb+nW (n=2,...,6) final
state signatures.Comment: 23 pages, 6 figures, v2: some issues clarified and references added.
To appear in JHE