Is it safe for me to switch from an 8GB server to a 4GB server? (Stats inside) We are looking to cut some of our server costs and the only place I think it might be possible is our db server.

We're currently running an 8GB rackspace cloud that houses a mysql instance and I believe is running a sphinx searchd instance as well.

Here are the stats from free -m:

       total       used       free     shared    buffers     cached
Mem:    7971       4748       3223          0        773       2773
-/+ buffers/cache: 1201       6769
Swap:  16378        467      15911


Here are the stats from top:

top - 15:23:52 up 349 days, 19:28,  1 user,  load average: 0.39, 0.72, 0.92
Tasks: 141 total,   1 running, 139 sleeping,   0 stopped,   1 zombie
Cpu(s):  0.5%us,  0.1%sy,  0.0%ni, 98.1%id,  1.3%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   8162332k total,  4861112k used,  3301220k free,   791832k buffers
Swap: 16771852k total,   478512k used, 16293340k free,  2839936k cached


It looks like were using just about half of our available 8Gigs but it would save us almost $200/mo if we could downgrade to a 4GB instance.

Any advice on this situation is much appreciated.

Thank You
It's possible. You will potentially lose capacity to serve all data requests from in memory buffers but that depends on how large your data is. 

select 
ROUND(SUM(data_length+index_length/pow(1024,2))) as TotalSizeMB, 
SUM(table_rows),
engine 
from information_schema.tables
where table_schema not in ('mysql','information_schema')
group by engine

to see your distribution per engine. You'll be able to judge whether all data and indexes fit inside the innodb bufferpool or indexes within the myisam key buffer. Assuming you set these buffers up yourself in the my.cnf config file and you're not running with the defaults.