SEOMike - 6:20 pm on Sep 29, 2011 (gmt 0) [edited by: SEOMike at 6:21 pm (utc) on Sep 29, 2011]
g1smd's got it right. A couple weeks ago I did a mass 410 culling for a client based on the same criteria. The site lost no ranking even though we literally cut 50% of the pages on the site. (Their main phrases climbed 3-4 spots in rankings, but I can't directly attribute that to the removal of junk pages since we made several simultaneous improvements.) The 410'd pages are slowly falling out of Google and their 410s are being removed from .htaccess as they drop out.
Aren't 301's bad though? I thought I read somewhere that google doesn't like to see 301's...or is that just links on your site to 301s
301s on their own aren't bad and actually do a great job of retaining the reputation for removed pages. In my opinion the most important use for them is for a site re-launch where page names and directory structures have changed. With old URLs 301'd to *proper* new pages, the new pages will quickly rank where the old ones did.
I don't have any direct evidence, but I suspect that if you have a lot of off-site links that get 301'd Google might think your site is a bit stale - HOWEVER, if the 301 is generated by canonicalization I doubt it would hurt.
[edited by: SEOMike at 6:21 pm (utc) on Sep 29, 2011]