What can I expect from a Minecraft Server running FTB with 3gbs of RAM?

What can I expect from a Minecraft Server running FTB with 3gbs of RAM?

My server has 3gb's of RAM. I have not the slightest clue what this means
for my server.
I'm interested in knowing what I can accomplish or allow on the server
with this amount of ram. Information I'm interested in includes but isn't
necessarily limited to, how many players can play at once before quality
of gameplay is hindered, how many estimated chunks could be realistically
loaded at one time before gameplay is hindered, what tasks or endeavors
use what is considered 'large amounts of ram' and how much ram is
considered a 'large amount'?
My server is running Feed The Beast, so please take this into
consideration with your calculations and estimates.