A "joke" I once heard was that after VLSI and ULSI, the industry felt that following the incresing desing complexity we would make us use all letters of the alphabet to describe new fanufacturable devices. So the description ideas behind SSI, MSI, LSI, VLSI and ULSI has been abandoned (like the 8086, 80186, 80286, 80386, 80486 Intel line of processors) and SoC (System-on-Chip) has been introduced to denote advanced VLSI devices, which integrate improved functionality, sometimes both analog and digital and even mechanical parts. SoCs are most of the times designed using IPs because of their complexity but the two terms are not equivalent. As far as for frequencies, they are technology and application dependent.