Re: How much different is 4 from 6 really,

Probably the biggest change between FCP 4 and 5 is the ability to edit multiclips. The biggest change from 5 to 6 was the Pro Rez codec which allowed those previously editing in uncompressed to have virtually the same quality but at much smaller file sizes. The smooth cam filter in FCP6 is also a great tool for toning down shaky footage. There are other improvements too numerous to mention (some newer codecs to handle the newer cameras), stability enhancements, etc. But if you're just shooting and editing with one camera and don't plan on hardware upgrades in the near future then stick with what you've got.

[andy shnikes] "and what is the difference from final cut studio form final cut pro? "

You need to go to the Apple web site and see for yourself. Final Cut Pro is a stand alone app and Final Cut Studio is a suite of pro apps:

Final Cut Pro
Compressor
DVD Studio Pro
LiveType
Motion
Cinema Tools
Soundtrack Pro
Color - a professional grading tool developed by Silicon Color and purchased by Apple. What used to cost 5000.00 USD for the HD version is now included in FCS2.

- Don