If you do it blind, YMMV. Mine did attempting similar things. I grew to distrust the upgrade option.
After a linuxfromscratch, I had a much better understanding. The real issue is that your toolchain consiste so: gcc; Kernel headers; & libc, usually glibc. Every binary is linked against libc.so.6 on the original system, and everything you compiled is likewise. In my slack 12 box (this) libc.so.6 is a symlink to libc-2.5.so. If the new system is linked against libc-2.6.so there might be big issues with anything you didn't upgrade. Likewise, compile errors have been traced to a mismatch of tools (wrong version of gcc or kernel headers).
So try it. The dodgy parts would be things like gnome, SDL, or k3b which utilise an awful lot of external libs. Straight GNU console stuff should be fine, unless your present versions are all compiled on the box.