Buffer & spring for a 7.5" 9mm AR pistol?

Would like to shoot subs and supers without changing out lower parts, and as fast and flat a shooter as possible ... if possible. Any recommendations?

Reading a thread on ar15.com recommending combined bolt/buffer weight in the ~22oz range and a "sliding weight" style buffer. So, I was looking for an ~8oz extended length buffer (titanium powder or weights) but can't find a good combo. Hoping to keep the price reasonable, so I didn't want to go the Taccom, Blitzkrieg, etc. route unless I really need to. But, the only buffer I could find close to that recommendation is a 10oz Kaw Valley. And, it's $80 once you get a spring to go with it. Any issue with a combined reciprocating weight of ~25oz with a 7.5" barrel? Any guidelines for reciprocating weight vs. barrel length?