In reply to Stone Muppet:
I've got a weight vest that you can add up to 30kg and is made of extremely strong stuff. Proper heavy duty. It isn't sand bags like other peoples but of individual weights... Not sure what they're made of, each weighs just under 1kg.
The only downside to this is it scratches the Hell out of my arms!
5kg can make quite a bit of difference. I'm one of those tall skinny climbers and normally climb 7b/v7 (indoor grading) and obviously depending on each centre's grading but at my local wall I do seem to drop about 3 grades roughly when bouldering. Which is demoralising but psyches me up to try harder.
I've done endurance top roping and could still manage a 6b+ after 14 consecutive routes. Truth be told I haven't actually tried doing more than 6c/v5 with the vest on... Would fail I think.
However in the short term I've used it I've seen a huge improvement, to the point I can now lock off campus for 10-15 secs on medium crimps with one arm, when I would struggle to even lock off a couple of weeks before!
Haven't had any comments or anything, other than being told I'm nuts/should be Russian and if they can try it out.
I like my vest, good investment!