Looking for very fast MCU, any advice?

Hello,

I am using a PIC18F4620 as an universal "workhorse" in many
applications
and I like this MCU because of its versatility and it's easy to use.

Recently I am experimenting with an USB-interface chip from FTDI. This
works nice
but now I am designing a multichannel ADC at high speed. The problem
now is that
the MCU is not fast enough to control the ADC-chip, buffer the data
and control the
USB-chip when working at a high througput.

Does anybody know about a faster replacement for the the PIC18F4620?
Requirements:

- about 100 MIPS
- easy housing, preferable DIP
- built in RAM and ROM
- easy (re)flashable

Any recommandations?

Regards, Teuniz