Will 40,000 301 redirects slow down a site? The 301 redirects will be from within the same site.
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We're using a plugin for this (Redirection WP) and the author mentioned this regarding the performance "The plugin works in a similar manner to how WordPress handles permalinks and should not result in any noticeable slowdown to your site."
Another thing too is he said "Apache .htaccess is not required - works entirely inside WordPress"