Custom fields for HTML personalisation - thoughts/questions

I'm currently using CM to send out an email to our customers, but I would like to add a high level of personalisation to each email.

Essentially there are going to be two large blocks of HTML in each email which are going to be different for every person.  I am thinking that maybe I could use CM's custom field feature to implement this, but was thinking:

* We have ~2500 people on the list at the moment, how feasible would it be to update the custom fields on all of these once per month?  Does anyone else do this?
* I am assuming that the custom fields are HTML-escaped?  Ideally I would like to just include the HTML from my system via a custom field, an "HTML" type would be very cool here, with the option of providing a plain text version too.   How do others achieve this?

Thanks!

Ross :)

200,000 companies around the world can't be wrong.

From Australia to Zimbabwe, and everywhere in between, companies count on 
Campaign Monitor for email campaigns that drive real business results.

Get started for free
1-888-533-8098