Lantiq xway mips CPU 34kc or 24kc?

Hardware Questions and Recommendations
1

I have a Buffalo WBMR-HP-G300H with an old version of openwrt. I'd like migrate to lede, so I see the differences between old and new config.
I see in CONFIG_DEFAULT_TARGET_OPTIMIZATION the parameter -mtune=24kc and in CONFIG_CPU_TYPE 24kc.
In my previous configuration I have 34kc and also in openwrt's wiki there is 34kc.
Why there are these changes? Also in other profiles with Lantiq xway the cpu is 24kc and not 34kc.
I don't know the differences between 24kc and 34kc, I'm a newbie on mips architecture.

Thank you for the clarification.

2

The 34 core should be backward compatible with 24 object code. The ar71xx directory and packages are all compiled for MIPS24kc, even for models that have 74kc chips.