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Seems at some point I've done this before with not so good outcome, any thoughts?
We have added about the same as you without any serious effect but we are talking about an 11 year old domain name as well.
I would play it safe and if at all possible stagger the pages over lets say a month if possible.
But bear in mind that high TrustRank sites can get away with actions that seem not to work for small sites.
I will be adding over 50,000 pages to a personal directory soon and won't be staggering the release. If it is good for the user, I do it.
I think this statement has a lot of merit. Google has different rules for different sites. Possibly their system triggers with percentage changes in no of pages which can explain many of the observations.