john1993:
speaking of which im surprised to hear ... that serial is faster than isp.
The difference is polling. With ISP, the target has to be polled for completion at the SPI bitrate #. With a bootloader the machine instruction that initiates programming simply completes.
flash page programming time is the real bottleneck.
Only after the programming circuitry is saturated.
# Or the programmer has to wait twice the erase-program time listed in the datasheet. Some AVR processors do not support polling for completion.