I have not been in schools that used this specific program, but I can give you some general thoughts about fluency, and what I was able to glean from my own quick internet search. Yes, the tool is often used for struggling readers, but, no, it is not designed exclusively, or even primarily, for remedial readers. (That application is, however, important for marketing purposes, which is why you will see RTI triangles attached to its promo materials.) Reading fluency is a skill that NT students continue to develop well into the secondary school years. Fluency at a grade 5 reading level does not automatically translate to fluency at an adult reading level. (Of course, I cannot speak to your son's actual level.)
Level 5 does equal grade 5, but even so his cwpm is way over the normative goal for grade 5 reading, and suggests that he should be moved up, probably one to two levels. One of the challenges, though, is that the program relies on partner reading, and it is highly doubtful that there is a dyslexic in his classroom reading fluently at the grade 4/5 level. He probably should be (if he isn't already) reading with an adult as his partner, which the program explicitly recommends for this situation.
The program has levels up through ninth grade, but the package he is using is only grades 4-6; the school may not have access to the higher level.
You may find this manual of interest. Please be considerate about test security, though, as it contains placement and progress monitoring exams. Links on this page to the primary (grades 1-3), intermediate (grades 4-6), and secondary (grades 7-9) manuals:
Index of Six Minute Solution Manuals http://www.wou.edu/~brownbr/Classes/The_Six_Minute_Solution/
