The quality of the transmitted signal, using any mode, declines over a period of time - typically within about two days of continuous operation.
For example: a single-tone (JT65-HF) digital mode TX signal will,
immediately after booting the radio, will be sound (on an external
receiver), look on the SmartSDR panadapter and appear on a spectrum
analyzer as expected. The signal will degrade to something
noisier and broader in, at most, two days of continuous operation and much faster when used in a complex (e.g. multiple panadapters) manner.
Receiving seems unaffected.
Rebooting the radio (and restarting SmartSDR as a precaution) restores the system to nominal condition, but eventually degrades again.
Relatively high, as I normally leave radios on for months (collecting spots, etc.) and I will invariably have to reboot the 6700 before attempting transmitting, taking several minutes.