I played around with booting from the SD card some years ago on my Sam 460ex - it's probably not different from the cr in this respect.
In fact, I had both a boot volume and a Work: volume on the SD card and no hard disk at all.
It worked well enough, but the speed was definitely slower than with a (conventional) hard disk.
I didn't try using an SSD on the 460, but I have always used SSDs on my 440ep, and that boots quite fast.
Best regards,
Niels