I briefly flew Let410 UVP-E in pax and cargo configurations.
we used to plan on TAS of 180kts.
with full main and aux (wing tip tanks) we had approx 1400kgs and based on 300 kg/hr consumption and reserves in mind we used to fly it on up to 4 hours legs= 720NM.
i do not recall the payload but i remember there is a fuel to payload penalty as the MZFW to MTOW was small.
hope this helps
