Here's some info that might help in your decision making process.
[link|http://news.com.com/2009-1001-823512.html|Commentary: IBM's Linux leanings]
Gartner Viewpoint
Special to CNET News.com
January 25, 2002, 2:30 PM PT
By Mike Chuba and John Phelps, Gartner Analysts

In the past year, Linux on the mainframe has moved from an outsider in the data center to a credible offering for select environments.

IBM continues to invest heavily in the promotion of Linux on the mainframe, as that operating system represents its best opportunity to capture new workloads for its mainframe business within the enterprise as well as with Internet service providers.
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[link|http://www.informationweek.com/story/IWK20020125S0001|
IBM To Offer Linux-Only Mainframe]
Informationweek.com
Jan. 25, 2002

Continuing its push into the Linux market, IBM Friday said it will begin selling a mainframe computer that uses the open-source operating system as its sole operating system.

IBM officials say the offering is aimed at businesses that use numerous smaller servers, such as those powered by a combination of Intel microprocessors and Microsoft's Windows operating system. Transferring the computing tasks handled by multiple servers onto a single mainframe, the company maintains, will help users lower their overall computing costs without sacrificing horsepower.
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A basic version of the Linux-only mainframe will start at about $400,000, including three years of maintenance, while the sticker price on an entry-level zOS-based mainframe starts at about $750,000.