sorry for the delay, it was a long day ..

I simply use tagential velocity v = angular velocity omega times radius r

(where assuming these are near the centre of the galaxy, then 'radius' is effectively the distance from us to the star)

I chose SO-26 since in 10 years it seems to tangentially-travel about 0.1 arcsecond (by comparison with the scale)

so tang vel v = [(0.1/3600)/10years] times 30,000 Light years .. approximately ..

and I get about 0.08, meaning around 8 percent of light speed for SO-26. That sounds about right, do you think ?

That's the tangential velocity .. for total vel of the star, I'd need radial velocity too, but I can't imagine what that is or whether it would be that great relative to us (woudn't the orbits around the black hole would be pretty tightly bounded?)

As for the tidal force .. I'd need the gravitational acceleration as a function, and get its gradient .. not sure about that one.

Thanks for posting Nick .. Daniel