Though Wells Fargo's hostile takeover bid for First Interstate Bancorp has whetted Wall Street's appetite for big operational cost savings, combining the banks' computer systems might prove to be difficult and even expensive, some observers said.

The $10.1 billion bid by San Francisco-based Wells for its downstate rival is largely hinged on expected cost savings of $700 million a year. Analysts said the cuts could come from eliminating as many as 150 overlapping branches and consolidating back-office facilities.

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