Can bukkit solve my problem?

I'm using vanilla server and i have problem with server lags, when i host 5 people (including me)
they have terrible lags and can't play (i'm talking about 1.8.1)
My internet speeds are:

My specs are :

Amd Phenom II 955 BOX 3.2Ghz X4

4Gb Ram

i also think the server runs on 32bit java and not the 64 one, how can i fix this ?
also i'm not sure the server uses All of my Resources...

can i use bukkit to improve my performance ?
all of the players i host are from my country.

 

Here is a useful tool.
http://canihostaminecraftserver.com/
It suggests no more than 3 players for your upload speed.

 

Ok, if i use a bukkit server i may get better preformance?
and what about using 64bit java?>
and opening ports ?

 

That site is very wrong in most cases. Your connection should be able to host double that....

 

so why i am not ?