An idea for a next release:
It might help to have OSCCAL as a parameter, I had it in the old bootloader, at the very beginning of main()
#ifdef OSC_CAL
// OSCCAL calibration for 8.000MHz internal OSC, Pito 29/4/2011
OSCCAL = OSC_CAL;
#endif
Then, for example, -DOSC_CAL=134 in the Makefile set the proper clock frequency so the upload (and the uart communication within the sketch) worked fine.
PS: to find the proper OSC_CAL is an another story, the values from 1-254 I tried in past did 5-15MHz OSC clock, nonlinear behavior, however.. 
P.