I am quite frankly astonished that you are asking on this forum for disk advice when you are developing a system that will process over 20K transactions per minute 24/7 on average!! See here for just a few of the things that make this level of processing difficult: http://sqlblog.com/blogs/paul_nielsen/archive/2007/12/12/10-lessons-from-35k-tps.aspx.

If you truly need that level of performance, you best get yourself a top-level DBA and get him/her involved in this from the ground up!! There are and incredible array of things that can/should be done/configured to achieve optimal performance of a SQL Server system - much more than just the disk system too. 🙂