Very muddy along the path to this one. It took me a few minutes to find the cache - I'm not sure why. I looked in the obvious place but didn't see it first time. So I went off looking in other places before returning and finding it.
I qualify for this as I have found 177 challenges so far and 33 of them are at difficulty 5. I've chosen 10 from those which I'm listing below, so now changing this to be a find.
GC1K9PZ Surrey Icon Challenge (D5.0/T1.5), found 11-Oct-2009
GC3C0H5 8-) The Lesser Date Challenge (D5.0/T2.5), found 12-Feb-2012
GC38FK4 #8 Wizardario's Challenge - !@#$%^&*()? (D5.0/T2.0), found 06-May-2012
GC45CJ5 Challenge Cache - BRONZE SILVER GOLD (D5.0/T2.5), found 18-Feb-2013
GC3DBR7 366 Challenge (D5.0/T2.5), found 05-May-2013
GC254H4 A Year, Lost! - 365 days of caching! - Challenge (D5.0/T5.0), found 01-Jun-2013
GC4B6RT 3 Corners T/D grid Challenge (D5.0/T2.0), found 01-Jun-2013
GC4N4BF 10 Challenges in a Day Challenge (D5.0/T2.5), found 14-Sep-2013
GC38X8Y The "Half-Jasmer" Challenge! (D5.0/T2.0), found 02-Aug-2014
GC2TVP8 M25 Junction 3 Challenge Cache: "Pay back time" (D5.0/T4.0), found 11-Aug-2014