The big runtime question?

[VillageIdiot]

Im struggling to figure out how long I will get on each run on the lipos.

I have tekin t8 rx8 combo with a 2050kv motor, 16pinion, 46 spur gear and 90c 6500mah lipos x2 to run 14.8v

now all the figures are out I cant find anywhere to calculate an rough/close figure of what runtime it will get before a battery change is required.

basically id light to know what runtimes id be getting and average mah usage per minute.

all the guides ive been finding give me stupid calculations like a 15mph top speed and 7 minute runs