LME nickel is just off overnight all-time highs but with prices in uncharted territory there's no limit to the market's upside, a trader says. Prices have been firmer on critically-tight global inventories and steady demand from the stainless sector, he notes. Short covering by fund, producer players also adds to the momentum. LME nickel trades last at $40,800 a metric ton, down 1% from the overnight high but up 4% from Friday's low.