Repeat after me: messing with the toolchain is bad, mmkay?
In all seriousness, the packages are built from the one repository. In this case that repository is glibc. So although you have 3, 4, 5 different glibc-* packages, they are all based off of one version. Changing a portion of glibc isn't going to be healthy, no matter how you look at it.
As it happens, glibc-solibs are the glibc shared libraries that are linked against by other programs.
That's not to say it's not possible to upgrade glibC: just double check your reasons for wanting to do so, first.
To be a little less flippant about the whole thing, and more educational:
Use something like partimage off a Knoppix-like distro to backup your box and then upgrade and see what happens. There's no need to take anyone's word for gospel, you can test it yourself - with minimal risks =)
# ... messing with the toolchain is bad, mmkay? ... messing with the toolchain is bad, mmkay? ... messing with the toolchain is bad, mmkay? ... #