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(Reuters) – Apple Inc (NASDAQ:AAPL) should affirm next week that its six-month-old iPad  tablet computer is selling well despite a shaky consumer market, while the iPhone continues to fend off a strong challenge from rival Google Inc.

Analysts expect fourth-quarter earnings next Monday to showcase Apple’s powerful one-two punch of the iPhone and the iPad, though some still question whether, with a plethora of rival products set to hit store shelves, Wall Street can justify Apple’s stratospheric valuation.

As has been the case for many quarters, iPhone growth will be the main driver, even as anticipation builds over an iPhone early next year tailor-made for the network of top mobile carrier Verizon Wireless — a move that would instantly boost Apple’s consumer reach in the United States.

Apple’s shares stand at a record high after breaking through the $300 mark for the first time this week. The company has so far proved resilient in the face of weak U.S. consumer spending. At the same time, gross margins should get a boost from falling component costs.

Although there is little doubt that September quarter numbers will be strong, investors have come to demand an outsized performance, so the bar is raised every three months.

Analysts say a big upside surprise may be tougher to achieve this time around given constraints in iPad and iPhone supply.

But the iPad is playing a bigger role in Apple’s business and could be a wild card this quarter, and Wall Street is eager to gauge consumer uptake of the tablet. While demand has been strong, manufacturing bottlenecks have limited production.

Apple trades at nearly 21 times forward earnings, a healthy premium over smartphone and PC rivals.