1810BM86 is a clone of Intel 8086 which was specified with round about 5 MHz
1810BM86M is a clone of 8086-2 which was specified with max. 8 MHz

The pictures of the debut say 1810BM86 !

I've never seen a 1810BM86 in original, because like mentioned above Robotron favored Siemens SAB clone due to better durability... But pictures in the web show an other case for 1810BM86 which is a kind of "divided" into three "parts". They have 2 cuts on the surface.

Thats why I think the cpus on the both pictures are from other manufacturer and later polished and relabeled with "1810BM86".

Thus it is possible, that cpus are specified with 8 MHz. But I do NOT exclude the possibility that cpus are original from russia and overclocked. Everything is possible...