Investec has upgraded power-systems giant Rolls-Royce from 'add' to 'buy', saying that profitability is on an upwards trajectory and higher payouts for shareholders could be on the cards."Rolls-Royce?s long-term and highly visible growth story is understood by the market. However, we argue its power, in terms of earnings potential, is underappreciated and only just coming to light," Investec said.Tradenext has reiterated its 'buy' rating for diversified miner and commodities trader Glencore Xstrata after the company signed $17.3bn of revolving credit facilities."The developments have created an ideal cut-price opportunity to buy into one of the largest diversified miners in the world. Our end-of-year target is 400p as cost-cutting measures and improved margins come through to boost profits," the broker said.UBS has upgraded its rating for property group Great Portland Estates from 'neutral' to 'buy', saying that the recent pull-back in the share price has created an opportunity to build positions.The broker highlighted that the business consistently outperform its cost of equity "a result of a strategy focused on buying, letting and selling buildings in two of Europe's strongest real estate markets". Meanwhile, earnings are expected to be boosted as current developments complete.