Great news!

Also, if you are using Melodyne on a really long track, it is definitely best to break it up into smaller clips.  Even on a 3 minute song, I edit vocals by phrase.

Good Day,
 
I guess OP found transpose function worked as desired in changing the pitch the desired amount and processing entire long track(s) in one swoop, but they did mention wanting 5th's and 7th's, which may not be the same thing, (i.e. harmonies) requiring reference to a certain scale, Minor or Major (or not what they meant seeing it worked). Melodyne may require a higher level of proficiency, but believe its one of its possible functions (but with which im not yet certain of or proficient with). However, while meant for vocal harmonies, Ive been able to generate up or down 2nd to 7th's, (normally up 3rd or 5th's), melodic instrument tracks, using Izotope Nectar harmony module, as a simple FX insert. Noting, best with melodic, single note, clean material and within a limited (vocal) bandwidth, such as a simple lead guitar, or piano harmony. Its fairly simple and easy to preview if its going to work, detects and suggests scale key, minor or major, and to solo only the harmony desired, and bounce it to new track, it does require high buffer setting. Again not likely good for polyphonic, and or distorted stuff, and may be hit and miss, but Ive generated some acceptable lead guitar harmonies with it, saving me figuring them out and recording separately. Noting also there may be some better dedicated harmony VST plugin's out there to do this(?), however I believe Nectar is an included FX with Sonar.
 
Cheers    

Little update:
As I stated, the way Colin explained is working well. For most of my use cases, it does what is to be done. The missing feature is the pitch correction at a cent-level. It does not sound important, BUT: The result differentiates like using a nice preamp vs. a cheapo-interface.
Melodyne analyzes the actual tuning very well. This allows me to fix detunes which I always have, because I am using a modular synth. Used "normally", this detune is nice. If a lot of tracks are mixed together, bad tuning s...ks.
 
I tried to record a track a couple of times (16 times - to be exact, which took me a hole week of my DAW-time...), than layer it and put the tracks into different areas of the stereo field. The result is a massive sound! If the tracks are detuned just a little bit, it gets noisy. But after fixing that with Melodyne, it is no problem any more: The timbre of the tracks are different, the formants of these tracks are intact.
Next step is the pitch shifting. I tried all the different algorithms, but even Radius-Mix is not as good for this job as Melodyne (OK, the difference is verrrrry small).
 
The "magic" wall where the plug-in is stopping seems to be one hour. Longer tracks let the system hang, but an hour is OK. Using Radius Mix, the speed is not really better - but stable even at two-hour-clips. Dave spoke about shorter clips, that is why I tried it. He is right...
 
I am sure that my use-case is not what the developers of Melodyne thought about and this is, why I can't expect issue-free processing of such long clips/tracks.
Thanks again for all the helpful comments and ideas...

vdd
The "magic" wall where the plug-in is stopping seems to be one hour. Longer tracks let the system hang, but an hour is OK.

 
Only my opinion but I don't think the Melodyne developers ever intended the software to be used on something an hour long. That is a long time to be using Melodyne on a track (unless I misunderstood your post).
 
We all use this plug in differently, our needs are all different but I always looked at Melodyne as tool to fix selected issues, not to be used as a plug in for extended periods of time (or at least anything longer than 3-4 minutes).
Myself, I use the tool for correction and some pitch shifting but never as a plug in (used on a whole track, every track, exc). Like I said, we are all different have our own opinions, but once you start using a correction tool for the majority of your content, you lose that natural sounding element that gives material a personality.

You know, that is the beauty of creativity.  We each use the same tool in different ways.  One potter might use a hammer to build shelves to display her pottery.  Another might use a hammer to break his pottery up into shards to create a mosaic.