There is a new ec2 type of instance with huge memory option : 244G
http://aws.typepad.com/aws/2013/01/ec2-for-in-memory-computing-the-high-memory-cluster-eight-extra-large.html
How this can help you with scaling Firebird ?
There are the cache and memory settings For Firebird but is better to put the main full database on the fastest storage and that is RAM for the moment
On linux i can mount a partition in memory (Install ubuntu/debian)
sudo mkdir /mnt/ram
sudo mount -t ramfs -o size=200G ramfs /mnt/ram
mount to show you the partitions mounted
and then move your database into the ram partition
cp -rp /var/lib/firebird/2.5/data/slowdb.fdb /mnt/ram/fast.db
What about D from the ACID ?
In Firebird we have a nifty feature called Shadow that creates a life snapshots of the active database (Think of it as Replication in real time) so you can activate it and keep a safe database on the SSD/HDD
http://ibexpert.net/ibe/index.php?n=Doc.DatabaseShadow
That large instance could help you with the Firebird cache settings also the extra SSD could do wonders
Inspired by the stack overflow big fat server architecture for the SQL
http://highscalability.com/blog/2009/8/5/stack-overflow-architecture.html