Without even looking at your heart rate figures, I can tell you that you need to ride more miles! I have ridden about 4.5 times what you have this year (over very hilly terrain) and I wouldn't say that I am ready for a 'big climb' yet ...
As a matter of interest, where
is the big climb? If it is in the UK then it can't be
that big! The hardest would be something like Great Dun Fell or Bealach na Ba. If it is something like Mount Teide on Tenerife, then yes, that
would take a lot of training to prepare for (unless you used very low gears and took all day to climb it).