Does this core generate an optimized version for the tinys (to fit in the small flashes).
The documentation in the boards.txt is really good (especially the fuse-settings).
What about the "empty" bootloader specification? Is this only to set the right fuses, not to upload a bootloader?
Fine, you are the programmer?
Your core is really better the code is smaller.
Now I unaderstand a bit more AVR-language.