Lemme just clear this once and for all.
FPS means Frames Per Second, basically it means how fast your computer can analyze the data sent to your client and make it visible. This is 95% dependant on your PC and 5% dependent on the server.
If you're having low FPS on JUST our server, that means you have a weak CPU or GPU (Ram really doesn't change your FPS).
Now lets talk about latency or better known as 'ping' (Which is the wrong way of saying it BTW).
Latency is NOT related to speed, you can have super duper massive speed but high (high means bad) latency.
This is how latency works:
Lets assume we have 100 ms latency (ping).
Client: Hi cowcraft.net I want to connect to your server, are you online?
After 0.1 seconds (100 ms) your message goes to cowcraft.net
Server: Hi client! Yes I'm online, you're welcome to join!
After 0.1 seconds this message gets sent to you.
This seneraio happens in every single thing you do for Minecraft. You break a block? It needs to tell the server you broke a block. You sent a message? It needs to tell the server you sent a message.
Now you can see, if this latency goes up a little too high, you'll have more 'lag'. There is no good or bad number in this case, some people can play easily with 300 ms latency, some scream LAG when they have 50 ms latency.
Do you want to find out what your latency is to the cowcraft network?
WindowsButton+R, type in cmd, type in ping cowcraft.net. Read the average time, thats your latency.
Open Terminal, type in ping cowcraft.net. You can see your latency there.
On one more note, people who live in Ocenia, you're going to have high latency no matter what, even if you directly have access to the main fibre that comes into your country, light's speed is limited, and you won't be able to make it better unless you move to another continent
Now why does everyone say YOU NEED MORE RAM FOR BETTER PERFORMANCE? Well, what minecraft does to make you lag less is, they store (cache) all the information from the server on your RAM (Random Access Memory). The more it is, the less it needs to flush (clear) that data to make space for new data. If this flushing happens too much you'll start getting random lag spikes, however a better GPU or CPU can help lower this "spike".
If you live in Canada or America and have high latency with the server, more than 200, contact your ISP (Internet Service Provider) and tell them about your problem, its nothing we can solve and its all because of your ISP.
If you live in Europe and have a latency higher than 300, you should contact your ISP as well.
Oh, just so you know, Optifine helps with your PC side of issues, it won't make your latency any lower.
~Amir, the CowCraft developer