Welcome to the forums.
Several years ago, I had Polk RT-800 mains, CS-300 center and FX500 surrounds. I was pleased with the sound until I purchased a pair of Klipsch CF-2's. The clarity & detail blew the polks away so I immediately sold them and bought a KV-3 center. From there, there was no turning back. I even demoed Polk's high end LSi series and still did not feel it came close to the sound I achieved with Klipsch.
As far as version IV vs V, take a look at my RF-7 vs RF-7ii vs RF-83 thread. It is not a night and day difference between those three but they do sound different. If you are comparing RF-62 to RF-62ii, I doubt you will hear much difference at all. It really depends on what is important to you. If you don't mind used speakers, you can get some unbelievable deals (ie RF-7ii System: the Best Deal of My Life).
I've always preferred the sound of the RF-82 and higher speakers. The smaller drivers of the RF-52 and RF-62 just didn't do it for me. If you are patient, you can get a killer deal on some killer speakers get more than you ever dreamed you would own.