Hi again,
Laktica:
the most helpful reply I've had in this forum, I really appreciate your response, THANKS!
You're welcome. thanx 
Laktica:
For EPROM you mentioned "Depending on the frequency you'd be expecting patches to be written, that could be quite acceptable." but I don't see why, Is it because during the 1/3 sec the sketch can't do anything else (i.e. the sequencer timing will stutter) or are you relating to the actual data incoming/outgoing buffering issues with the EPROM? If its the latter I don't see it being a problem as I'll only want to save patches now and again, if its the former I will have to investigate some sort of 'SRAM buffer' as I mentioned above.
That depends very much on the implementation. You could of course write it a byte at a time and keep doing other things in between. This is the time cost of writing only, reading is faster but I didn't find a spec on that.
And remembering if you use PROGMEM you won't be able to have a user modify the patch and save what was changed, they'll effectively be presets only. PROGMEM is a way of storing data that you know the values of when you write your sketch, like constant strings or large lookup tables, without taking up SRAM until you need it. EEPROM is read/write during the runtime of your sketch so good for saving settings, high scores, logged sensor data, and other things that change during the run that your sketch needs to keep track of next time it's powered up.
Depends entirely on what you want to do. Lots of options. Cheers !
Geoff