I don't claim to know the bottle neck for re tuning though, factors like the speed of the SPI bus, and maybe some other oscillators may be slower. It is also important to keep in mind, as you write, that the radio has to stay for a while on a frequency in order to actually capture data.
If anybody from lime knows the minimum feasible re tuning speed it would be great if they can leave a comment here. Both for similar frequencies (e.g. to cover all of 2400 to 2480 for Bluetooth) and between bands far away e.g. 145 mhz / 430 mhz.
This may also be relevant for people implementing frequency hopping spread spectrum (if all packets doesn't fit inside the SDR passband).