Dingle - I'm gonna disagree with you on some points mate.... A rig should be blanced no matter what length it is... I fish the exact same hand posistion as you are talking about, with reel seat shaft between pinkie and ring finger, on all my Spinning set ups.... From my light spinning rig which is 7ft with a Fin Nor ISX 4000, to my 8ft Exage with a Stella 6000, to my jigging set ups which are 5'6" matched to the Stella 6000, and 5'7" matched to a Stella 20000, and my heavy popping rod, which is an 8'3" Carpenter which is matched to the Stella 20000. All these rods feel balanced because of the design of the rod and the plavemnet of the reel seat. All rods should be balanced... if they aren't then the reel seat placement is incorrect.
I do agree with you though on the extra effort when using a longer rod in some cases because of the added weight. However, I feel this is minimal... A longer lighter rod will enable you to throw smaller lures more easily without a doubt.
That being said, I feel the perfect length for light tackle spinning, is 7' to 8'6".