There was little in the way of detailed information on offer yesterday as Westpac and St George briefed the market on their proposed merger. One solid commitment was to bring the cost to income ratio of the combined group down below 40 per cent. A second was that the takeover would increease earnings per share in the third year, and would be "strongly accretive" in the years after that.Management of neither bank would be drawn on the likely savings from the agreed takeover of St George. More detailed forecasts may be made available following the completion of two weeks of due diligence by Westpac.Westpac chief executive Gail Kelly is selling the merger on the theme of many brands, one platform and promising efficiencies in the back office.The local banks have done a reasonable job over the past decade bringing costs down. Cost to income ratios have dropped from around 50 per cent to close to 40. But the banks are looking over their shoulders at the world's most efficient banks, which have cost to income ratios in the 30s.In their financial statements for the March 2008 half Westpac reported a cost to income ratio of 44.4 per cent and St George reported a sector-leading ratio of 42.5 per cent.A year from now if Westpac is able to maintain its current 12 per cent annual rate of growth in net operating income it will report income of $6.1 billion. And if St George maintains its current five per cent rate of growth in income it will report income of $1.8 billion.If expenses keep growing at the current rate (eight per cent for Westpac year on year and five per cent for St George) the combined group would report operating expenses of $3.3 billion.The cost to income ratio would be around 42 per cent. To get it down to the 40 per cent target the merged bank would have to cut expenses by about $140 million.This is a pretty modest saving, at less than 10 per cent of the operating cost base of St George (though more than 11 per cent of the cost base of the bank's banking businesses alone).Presumably twice this level of saving is achievable. And were Westpac closing overlapping St George branches (which it insists it won't be) three times this level of savings might be feasible.While Kelly is promising to keep all the branches open and maintain customer-facing staff numbers, there is no escaping the fact that the main source of any aggressive cost savings would still have to come through cuts to staff expenses.More than half of Westpac's $2.4 billion of expenses in the March half were salaries and other staff expenses ($1.4 billion). And most of the $180 million increase in expenses over the past year was due to salaries and other staff expenses ($155 million).In St George's case staff expenses accounted for $421 million of the $716 million of expenses reported in the March half and accounted for $24 million of the $33 million