Increase max-cache-size

[Prabhat Rana]

I'm running BIND 9.5.1b1 on Solaris 10. Initially I didn't have any 'max-cache-size' parameter set in named.conf. When I was getting 1500 or more rercursive clients at any given time according to 'rndc status', I noticed some latency in recursive requests. I added the 'max-cache-size  500M;' and that seemed to help the latency because the number of lookups to the internet was reduced due to most of the request being fulfilled by the cache. I still have 25G Memory free. So my questions are. 
Where does the named cache sit? in memory? 
What is the max-cache-size by default?
What is the max value I can assign for cache?
I understand if I increase the size of cache it increases the security risks for cache poisoning. But I need to increase is so that as much possible queries are served by the cache
Any help would be greatly appreciated.
Prabhat
TSE
Sprint/Nextel