Looks like mountnman beat me to it. I walked it from Jenolan caves back to Katoomba, ie the reverse direction to what is commonly done.
Yes, the “huge climb” people refer to is really just a relentless steep walk up to the top of the Black Range. It’s all on FT, nothing technical, but would be strenuous with a heavy pack. I walked down it so missed that bit of fun, but walking either direction probably requires a similar level of effort.
You could also have a look at these distances by the Six Foot Track Marathon organisers, as they claim to be measured accurately:
http://www.sixfoot.com/course.php+1 the official map is quite useful. Also
http://www.wildwalks.com has track notes and maps but I can’t access the site at present.
p.s If walking from Katoomba Railway Station to the Explorers Marked Tree, you need to add about 2 km.