I agree with both of the above responses that suggest a more comprehensive outline of the potential variables is essential.
For example, in the quote above, you have made a determination (which we will assume is reasonable), that converting 1 of every 11,064 users at $25 subscription will allow you to take the site entirely to a subscription model. 1/100th of 1% conversion from user to subscriber will work for you. Presuming quality site and content - AND that content is updated regularly enough that one would want to be subscribed in order to 'keep up' - it sounds fine. You should be able to far exceed you conversion rate minimum.
Now you are a subscription site. But 11,000 users just got shut out for every subscriber converted. Where is that traffic going to go? If another site can now (or will) adopt these users, is your site good enough to survive the free site(s) which just picked up how many thousands of users that will be unhappy that your site kicked them out?
Now that you are a subscription site, can you keep the fresh content coming to retain your base? If the content isn't fresh and always updating, they will not feel a need to renew. Even among dedicated and happy users there will be a churn rate. People move on to other interests. I can't afford to pay for everything that I would like to do - so I have to pick and choose. Maybe the free competitor(s) aren't as good as you are - but maybe they are 'good enough' if free.
Now that you have jettisoned thousands of users that did not subscribe, how will you build your base? How will you grow? It would take a strong recommendation from someone I really trusted to sign up 'blind'.
Where will the new business come from? What will it cost to get?
Murdoch is part brilliant and part lunatic. This should be kept in mind.
Your post indicates going 100% subscription. IMO, unless you've really got something special, you would sink like the Bismarck.
Do you compromise and offer a 'taste' in a free area, and keep the really good stuff for subscribers? This would be a completely different approach than what was suggested in the OP.
I think that the delay in repsonse on this post is that it was considered an incomplete thought and not taken as seriously as expected.
WebmasterWorld would be an excellent comparative. Would it survive if 'all subscription'? What is the subscription rate of unique users to subscribers?
IMO, in many of these forums the last answer you are going to get is the truth, so there are certainly people with specific knowledge that just aren't going to say anything. 'Sharing' only goes so far here. On some topics I don't believe a word of anything from anyone. The BS can be neck deep.
There is a lot more to consider than the formula that you put forth.