1.>The Dalek's have been able to get past stairs since the 1980's.
Although only shown in the 80's, Daleks have ascended stairs before then. Way back in their third appearance, 'The Chase', Daleks were shown in locations they could only reach by ascending stairs.
1. they hover, they still don't climb them.
2. he's still one guy, with no superpowers, superstrength, etc.
1) Your point being? What tactical advantage does physically climbing stairs offer that hovering does not? Daleks are capable of high speed flight. How will a Borg assimilate them when they stay out of reach?
2) The only times the Borg have been stopped, it's by people without superpowers, superstrength, etc.