Umm I not a number geek enough to answer but I consider hilly anything west of me in the "Texas Hill Country". I personally live on a plateau but can venture just a bit to find hills.

If I am sore after a ride it was either hilly or windy. I have sent one visiting TE'r on my favorite ride just a bit west and she was sore like I am every time I do it. I don't know the stats on it though.

I don't ride mountains but when the mood strikes me I can find some lumpy rides.