* Impact of yen to start filtering through this quarter. * Japanese exporters typically hedge 3 months ahead. * Some analysts see risk that market too optimistic on yen impact. Currency hedging cost Japanese companies such as Honda Motor Co the chance to fully cash in on a weak yen last quarter, raising the risk that investor expectations could outrun earnings. The near 20 percent fall in the currency since October has been a primary driver of the longest weekly run of gains for the benchmark Nikkei index since 1959. But exporters may have been caught out by the magnitude of the yen's fall and bought too early, ... (full story)