The MachOX3 data sheet is an interesting read. Haven't compared FPGA's between vendors before, it's interesting to see what features they include.
The Mach family seem comparable with the bottom end of the Xilinx Spartan 3 family, both are LUT4. The on chip flash is nice, as is the i2c peripheral. Not so sure about the spi port, pretty easy to create one of these from fabric.
Block memories are comparable between the two. A major difference is dedicated multiplier hardware, absent in the Mach chip.
I think you may be underselling the board Derryn, you can do a fair bit with 6900 LUTS. A soft core processor is certainly doable. My Apple2FPGA project uses 15% of the LUTS (~2400) in a Xilinx XC3S1000. That includes the 6502 plus video controller. There would probably be enough memory in the Mach to simulate the 8k ROMs plus 16k of RAM. The S1000 can do 2x8k ROM plus 48k RAM.