If you just want to get a PQR off of the particular size pipe you are using in production, you can do that.  If you use a pipe size other then what is listed in the standard pipe size column, you will need to follow what falls to the right of job size pipe for your range of qualification.  If you do a PQR with a 2" or 3" and 6" or 8" standard pipe size, then you will have a very big qualification range ( see to the right of standard pipe sizes for range of qaulification). Hope this helped a bit.