I saw a couple of research specials about the "RUS", which in turn caused me to read a little on them as well. Rus is just the russian word for Viking. While Russia means land conquered by vikings.
The RUS were swedish. They did not refer to themselves as Rus, their victims did.Put more simply there is no such they as Rus, ancient or otherwise, since they never called themselves that. They used swedish ship building techniques, and for generations moved back and forth between "russia", Finland, sweden, etc. They did not cut themselves off from their nation of origin until several centuries had passed. They met with and traded with the Swedish Vikings as they would with cousins and equals. Their ships remained viking longships. Some of them were small in scale, but the same is true of the other vikings. Viking longships were not 1 size fits all. Some were capable of holding 10 times the troops that others could hold.
I think using one of the viking longboats for the RUS is completely accurate. There are 3-4 different models out there. Just find one and use that.
One thing I do is give the viking clans two longboats. 1 capable of holding 1 unit, which replaces the Curragh, canoe, etc.
But reguardless of size all viking ships (including the "Rus") had the same characteristics (reguardless of size) they could obtain great speed (due to the hydroplaning of their hulls), they had a very shallow draft, and could sail in very small rivers. They had great agility due to their unique rigging. And they were extremely seaworthy (crossing the atlantic, etc) due to their clinker-hull flexing and swimming through the waves rather then fighting them.