I need a 1/4" x 1 1/2" x 80" steel flat bar.  I will omit the details of what I need it for because this question is basically asking which composition yields a stronger steel.

www.discountsteel.com has a wide variety of steel bars, but I am not sure how to read the ratings regarding tensil strength and hardness.  Here are all the products:

http://www.discountsteel.com/items/304_Stainless_Steel_Flat_Bar.cfm
http://www.discountsteel.com/items/1018_Cold_Rolled_Steel_Flat_Bar.cfm
http://www.discountsteel.com/items/A36_Hot_Rolled_Steel_Flat_Bar.cfm

If you click the ASTM material Specifications tab at the bottom of the pages and scroll to the bottom, you will see mechanical data for which I have the following questions:

First off, what is "*minimum* tensil strength"?  The stainless steel 304 has a minimum of 75, but the hot rolled and cold rolled appear to have ranges of 58-80 and 55-70 respectively.  Why does stainless have a single number and the others have ranges?  Why does it says *minimum*?  Does a higher number mean stronger steel?

What is minimum yield strength?

Second is the hardness scale which uses the Rockwell scale which I've looked into a bit.  The stainless rating for 304 is 88, but the rating for hot-rolled is B76.  For cold-rolled, it seems to be broken into two:  Hot rolled is B67-B80 and cold drawn is B80-B90.  This confuses me even more because this looks like the steel is cold rolled hot rolled?  Why is the stainless rating just 88 while the others seem to be a range and use the B scale?  Does stainless just default to a scale since it's just represented by a raw number?