Do you need to change the URL, or can you repurpose the high-ranking URL instead?
In other words, change of content that is still related to the old content, rather than a permanent redirect. PageRank will drop as far a Google is concerned, but 85% is not as good as 100% but way better than 0%. Of course any giant changes in other areas can have an effect as well. But 85% is not as good as 100% but better than the alternative.
If you think about it, a 301 redirect should have a little impact on the ranking, at least, and here's why: for external links into the website, now killed and served up as a new page.
Google has had for a few years now, at least has been reported to have a minimum of 15% penalty, or better stated 85% passthrough if you cannot keep the original URL. Only 85% of the page rank is retained as a penalty for not keeping the golden rule never ever change an URL EVER.
If you bought it for its page rank, you lose 15% instantly for gobbling it up. It makes sense.
Reason for penalty, and it might be much higher than 15% now: there is no legitimate reason as far as Google is concerned for changing an URL, unless you are shortening your website domain name, but KEEP the Old long one and permanently redirect it to the new folder of the shorter domain name.
In any case there is a hit on ranking to say convert one system to another: .asp to .php, .html to .php etc.
Another fix is NOT to 301 redirect with HTML where ranking is important but keep it(them) if it is worth it for you to have the server process a certain extension as a .php extension if it can, if changing extensions is your reason to redirect.
An unknown penalty hit is to make you think twice about plying games: I don't think anyone knows how big the hit is now: If done for the wrong purpose, the hit is registering your website as SPAM (perhaps a 20000% hit on the ENTIRE website, not just the page(s) in question.
For more information on the negative consequences here is a link to another thread in this forum recently:
Does purposely linking to an invalid URL and then using 301 affect SEO?
Google wants webmasters thinking of content, not gaming-masters-of-ranking. That's why they will not release Google Ranks anymore.