What is a key-value memory storage system that is not intended to be persistent, but can store over 1MB?
Have you considered memcached?
What are your requirements? A very large object cache is better suited for things like varnish where latency isn't the most important part of the system memcached will happily store your 25MB objects, but it won't be noticeably faster than using something else since more time will be spent transferring the object than locating it.