The 630's VRAM is soldered onto the logic board, whereas others have a VRAM socket for upgrades (FYI in case you were not aware.)
I have no experience with the Spicy-O-Clock but my 630 was overclocked to 40MHz and my LC475 to 33MHz using the resistor moving method. Both have full '040's, both are rock solid stable and have been for many years. I am really impressed with the 630 in particular at 40MHz, it's no PowerMac but OS 8.1 and most applications from that time period are very responsive. Not that I'm sure 45MHz wouldn't impress me even more, I'm just not sure it's really necessary for anything other than bragging rights.