Server issue and general help!

Hey guys, new-ish to hosting a server here. Let me start by posting my specs; Zambezi Bulldozer 6 true core AMD CPU @3.3ghz, 8gigs of 1333mhz RAM(2x4g) No other components matter to my understanding but I also run an EVGA Nvidia GTX 650 GPU, mobo is an ASUS LX-3 AMD+ with a 750w modular PSU, and yes it is 80 bronze. One 80gig SATA 2 HDD at 7200 RPM I use for server files only, and 2 additional 160 gig SATA 2 HDD at 7500rpm I use for other. Also here is a link to my internet speeds http://www.speedtest.net/my-result/2824618737

Now down to my problem. I get the frequent console message "WARNING! Server can't keep up!" and I must say I looked around a lot about this and I am still baffled. I have 8 gigs of ram to offer my server and my CPU isnt the worst, even if the server utilize 1 core as I read, it's still clocked at 3.3ghz, that isn't too bad! I guess I should tell you it's a 20 man server but I will have at most roughly 10 people on at a time. I allocated more ram to the server by changing Xmx- 1024m to Xmx- 4g to at least try and use half my RAM, which ALL CPU Meter shows me at most my server ever used was 44% of my RAM. Why am I getting this error? I have more RAM then my server is using?

Maybe someone here can clarify this for me, because I am starting to get frustrated. Thanks in advance.

 

Can't keep up messages can occur if your TPS dips below 20 for any reason. This could be caused by chunk generation, mobs/animals, plugins or a wide variety of other things. I suggest using TheCleaner and run "/clean --vitals" to see what your TPS is at, what your entity count is like, and how many chunks you have loaded.

 

It could be a problem with your internet service. I'm not completely sure but if your internet connection speed is low then those sort of messages can occur. When I had these problems on my server, I plugged in an Ethernet cable and the messages stopped. Could be just me, but I would try it! If you already connect with Ethernet, then I would advise investing in a new Internet service.

 

I would like to upgrade to a better service with greater upload speeds, my dilemma however is right now my current internet plan has no usage cap, every plan above where I am now has a cap set at 250gb a month. I am unsure how much a small minecraft server will run me in usage per month. I normally have between 4 - 8 approx. online with maybe 4 hours where no one is online. I am afraid to upgrade my ISP at risk of going over my limit. Any insight on how much bandwidth a server of, we'll say to be safe, 10 people on 24/7 for 1 month would cost me in internet usage?

If my TPS is dipping below 20 is there a fix for this?

Also, side note here, anyone else notice with the 1.6.2 craftbukkit dev build people are getting random disconnects, or is that just on my end? Thanks.