I see you have reading comprehension issues.
1953 IBM gave us the boat anchor 701 EDPM Computer it was a good decade before they had anything that lived up to their hype
Their entry into the PC world: 1974 IBM 5100 personal computer sucked equally hard. They never did ever figure PCs out.
Nobody "overclocks" a mainframe and yes after almost 60 years they are fairly stable, and over priced and obsolete. I find the irony that they are now running linux almost hysterical.
There's no money in it. Regular systems have gotten so powerful that a 1u server can handel what used to need a main frame or mini. Why do you think all the old mainframe and mini people are gone or scaled way back? IBM's mainframes are mainly living on legacy and nitch, but I wouldn't say there is no competition.
http://www.cray.com/products/XT5m.aspx
http://www.sgi.com/products/servers/altix/ice/
http://www.nec.com/de/en/prod/servers/hpc/index.html
http://www.unisys.com/unisys/theme/index.jsp?id=16000034
http://h20223.www2.hp.com/nonstopcomputing/cache/76385-0-0-225-121.html
http://www.bull.com/products/servers.html
http://ts.fujitsu.com/products/bs2000/index.html
Hp also owns DEC and Oracle will soon own Sun.
However big iron is pretty much dead. HPC (aka Beowulf) clusters pretty much have replaced them for most functions and they are significantly cheaper and far more flexible.
None of those companies were ever mainframe companies. But intel has made inroads via HPC clusters and AMD's price/perfomance/power has made it popular recently.
Suuure, just like it did with the PC and its hard drives and its cpus and its printers. IBM has never understood the consumer market and it really doesn't understand the SMB market. But it sure can sell to big business and the government.
You might want to check out
http://www.top500.org/list/2009/06/100