My situation is different from yours, but this is how I do it.
I also have the 5th gen, as well as 2nd gen Nano, and 2 generations of Touches. Having all of these, I don't feel the need to carry around my entire music collection, which stands right now at 20GB audio and a whole lot more video. If I rip the rest of my cd collection, I could have close to 150GB. That probably won't happen since I'm pretty sure I won't listen to it.
I find myself carrying around my 16GB 2nd generation Touch much more than everything else. Half is devoted to video - movies, tv, video podcasts. The other half is audio - books, music, podcasts. And the music I put on it are selected playlists, which I do a lot of. I also keep different playlists on the other older Touch and the Nano, while the 5th generation has all of my ripped music.
My opinion? Go for the smaller and sleeker. You don't necessarily need to carry all of your music. You still have that 5th generation and it still has room to spare (I take it you got the 30GB?) You can always get that Classic at a later date, if you feel the need.
My iTunes library is about 14 GB so a nano would have very little upgrade room for music. But the Nano is much smaller and sleeker. I already has a 5th gen which is almost the same thing as a Classic but a classic has all the storage you could want. The classic is also bulkier though. Any thoughts on what you would choose in this situation?