There are two things mixed up over at reddit. It is a little confusing:
- The higher clock frequency and L2 cache of the new 3DS mentioned there may lead to better performance in 3DS-games / in CTR-mode (CTR-001 is the first 3DS). New 3DS has a quad-core ARM11 with 804MHz and old 3DS dual-core ARM11 with 268 MHz. 3DS-games run on the ARM11.
- When using TWiLight Menu++, the 3DS boots into TWL-mode (TWL-001 is the DSi). Both, the old and new 3DS have an additional 133MHz ARM9 single-core processor, which is (among other things) used for compatibility to DS(i)-games.
The original DS and DS-lite had a 67MHz ARM9, while the DSi already had 133MHz.
To cut a long story short: ALL models of 2/3DS/DSi can apply the higher 133MHz speed to regular DS-games with TWiLight Menu++ and this
may lead to better performance in
DS-games.
The higher ARM9 clock feature is not tied to using a Slot-1 card. On the contrary: The settings explicitly mention that the higher CPU clock will not be used if the Slot-1 card is launched with the “reboot” method.