I've just come back from my El Chorro trip following about 6 weeks endurance-focus 'training'. If anyone's interested, this is how it went for me.
Each week I generally achieved one routes session doing double laps on routes, up to my onsight level. I would have done 4x4s but didn't feel achievable in overcrowded Westway on Tuesdays/Thursdays. I supplemented this with one 'boulder PE' session, where I either did 4xs on boulders (also hard at crowded wall) or boulder circuits up to about 50 moves. I never felt I got the balance right on these - was either going at boulders too hard and falling off half-way in my circuit or too easy and not feeling super-pumped. I also kept one boulder session a week going as I didn't want to lose the strength gains I'd made over the autumn/winter. I think this was successful.
I found that as the weeks went on I was feeling drained and less sharp. Had a lot of work on and probably never got 8 hours sleep on any worknight in the last month of training. As I was feeling tired a lot of the time I decided not to add any other training sessions, eg. fingerboard training sessions (I was also carrying finger injuries into the training cycle). The last 2 weeks of training I felt I achieved about 3 good sessions out of 6. My last routes endurance session I achieved my top performance grade/difficulty wise, but my overall volume had dropped. My last training session was a good hard outdoor bouldering session where I was pleased with my performance (one grade below PB). I then had a week where I just stretched and did antagonist exercises. This was good as I was aching all week from the boulder session on Sunday.
In El Chorro I felt quite fit (but not fit enough for the 30m routes), and strong enough to pull on most of the moves I tried. What I struggled with was mind - hadn't done routes outside for four months or more and was finding it difficult to deal with runouts. Also was finding it hard route-reading and using my feet well. Too much plastic pulling! In the first days of the holiday I just didn't perform up to my expectations or my usual standard. On the second last day I had a day of easy volume which I really enjoyed. On the last day I matched my personal best redpoint of F7b (though this one was almost certainly 7a+). Ultimately, I was pleased with how I was climbing by the last day of the trip. If I'd had another week I might have actually started climbing well!
What I'd do differently for another trip: more falling practice before going. More easy volume in the first few days of holiday to get my head in gear and my route-reading working better. More sleep in run up to holiday to recover from training. Rehab injuries effectively and not just add training volume and hope. Do boulder circuits more than 4x4s. Train at less busy times where possible and do routes up-down-up. This sort of pump replicates the feeling I get on outdoor routes more than doing a route twice.
My plan now is to focus on rehab for my injuries but try to keep climbing indoors and out on easier stuff so I don't completely lose my gains.
Hope this long rambling post helps others in their endurance training plans in the future.