ESP32 Rover module advice.

[Sprite]

You are right the 4 bit is for MMC and not SD card. I will be using standard SD cards and I believe a max speed of 80Mhz can be achieved.

MMC has nothing to do with this. 4-bit SPI is for quad-SPI capable devices. This includes NOR flash chips, but not MMC/SD.

But can this also be reduced for on the same SPI I got other device which do not need to fast speed?

I don't get that comment.

As this is a new board, we aim to design it for max performance.

I will be using the SD card as temp storage for Audio and possibly Videos/Photos in the future.

You should use the SDMMC Host peripheral then, not the SPI peripherals. Suggest you read at least the top part of this.

[djoshi]

Sorry what i meant to say is

If the SPI is being used by multiple devices. Can I reduce the speed from 80 MHz to much slower, when not required?

What is the difference between SDMMC Host Driver and SD SPI Host Driver ? We aim to use microSD card.

[Sprite]

If the SPI is being used by multiple devices. Can I reduce the speed from 80 MHz to much slower, when not required?

If you use ESP-IDF, yes; you can configure each device on a bus to have its own clock speed.

What is the difference between SDMMC Host Driver and SD SPI Host Driver ? We aim to use microSD card.

SD-cards natively speak the SDMMC protocol; that is how you get the most speed out of them and that is where they are the most compatible with. They mostly also can speak SPI, but it's slower and technically support for it is optional.