Ji
can't see your email, think you need to make it visible in your profile.
Lee Quarry is about 45mins from Gisburn (I live about 2 miles form the quarry), so it's quite do-able in a day. Route from Lee Quarry is a bit convoluted though, lots of narrow lanes so plan your route before hand.
As for the grading, B.A.Nana is right about the Black gulley, it's really red but they decided on black due to the consequences of getting it wrong, not sure I fully agree but that was the reasoning behind the decision. However I would say most of the red is more difficult than a lot of the Llandegla black for example. The black stuff up at Whelpstone Crag is proper black due to it's techincal nature. I think the main difference between the blue and the red is there are no steep short climbs on the blue, the trail doesn't drop below a metre wide and there are no rocky sections, it's all well surfaced.
I think the thing that is different to many trail centres is that they have graded individual sections rather than the whole route, which actually makes some sense.