Well I would like to report a successful 1284P installation, so I will. 
I'm using CrossRoads great through-hole Bobuino board and so far no signs of serial uploading problem using a 68K big sketch on repeated tries, no errors reported or seen.
So I would like to thank CrossRoads for designing, building, and selling a great blank PCB that will support 644P and 1284P chips, and a big hand to Nick's great bootloader program that kept me from having to purchase a more capable hardware programmer then the USBtiny that I do have.
So my Arduino (well one of them anyway) now has 16K of SRAM, how large is yours? 
Lefty