For the 644? If so I use opto version set up for 16mhz named optiboot_atmega644p-4-5.hex, as it's the smallest and fastest baudrate, handles WDT interrupts properly, etc.
Yes Sorry for the 644 
cool thanks a lot for posting that. I'll give it a go.
But be aware that the bobuino uses a different pins_arduino.h file as he changes some of the pin layout to better match the standard shield layout.
Noted (well printed out)
Just burnt a bootloader to the ATMega644P using the Sanguino whatsit thingy via the ISP so thanks for giving me the confidence and indeed the knowledge to try it. Also just uploaded via USB a test sketch to my prototype and all is well as it is working faultlessly. I did spot an error in that the rst pin must not be through the 0.1uf cap and my wire went the wrong side - stupid as when I did that wire I knew it had to bypass it so my excuse is that I was tired at the time...
I can't thank everyone enough for your help, confidence building and support through what was for me a very frustrating few days - your all fantastic and this is the best forum for this subject I have come across. VERY much appreciated!!!
Gonna try a 644PA next - fingers crossed!
All the very best
Steve