A 99105 breakout board for the Cortex does not immediately make sense. From Stuart's measurements, a 99xxx is about 15% faster than a 9995, when both are running without wait states on a 16 bit bus and at 3 MHz (i.e. 9995 code and workspace on the internal RAM). When code and and workspace are in main RAM the difference goes up to about 60% faster. Putting the 99xxx on 6 MHz makes it 1.6 x 2 = ~3 times faster.
But that all assumes zero-wait state memory. The memory circuit on a Cortex can only deliver one byte every 650ns or so. A 6 MHz 99xxx would need about 7 wait states for two bytes to be delivered from RAM. Taking that into account, the breakout board is more likely to be back in the 15% performance difference area. You could of course integrate fast RAM onto the board and use it as a kind of co-processor, perhaps hooked up to the E-Bus.
Paul