Heating Capacity of Mitsubishi Mini-splits

Bleg on Minisplit Ductless Airsource Heat Pumps

Sources have told me that in the last few years it has become possible to heat buildings in cold climates (eg the US northeast) with the latest generation of ductless minisplit air-source heat pumps.  I am seeking detailed technical information on the performance of these kinds of systems that would allow me to evaluate the low temperature limits, thermodynamic efficiency, and cost-effectiveness of doing this in a retrofit context.  I haven't easily come up with sufficiently detailed information in Googling around - can any readers point me in the right direction?