Running Minecraft server + client on same computer

[AV3Nguyen]

Hello, my system:
CPU: I5-4690k overclocked @ 4.5ghz
GPU: MSI Gaming GTX 970 (not overclocked when playing minecraft)
RAM: 2x4GB DDR3-1600 (G.Skill Sniper Series)

(From speedtest.net, two tests. ethernet all the way to modem)
Ping: 16, 15
DL Speed: 30.17 Mbps, 30.61 Mbps
UL Speed: 0.86 Mbps, 0.93 Mbps

From MSI Afterburner:
Peak GPU usage: 42%
Peak RAM: 7669 MB
Peak VRAM: 1397MB
CPU Usage: 90% on average across all 4 cores

I'm running a minecraft server and client (with tekkit modpack) and I've noticed that I'm stuttering like mad when I'm playing. The server is a small private one with 3 people playing at once at most, usually only 2 people. It would be nice to know where the bottleneck is, since a 970 is way more than enough to run minecraft completely smoothly at 1080p. Also, for that bottleneck, what would be the best method of fixing it? E.g. if it is a CPU bottleneck, what would be a good CPU to upgrade to?

inb4: I play many other games than minecraft, thats why I have such a strong GPU.

Thanks for your time! If there's any aspect of my system that needs to be known, say so and I'll post it.

Edit: Chrome was the problem. I closed it and it's running smoothly.

 

[dudeman509]

Open Task Manager, and then open Resource Monitor from the performance tab. Monitor CPU usage and disk activity while playing.

I am wondering if the problem may lie in your crappy upload speed, though. Who's your ISP?

 

[Xphonyd]

Is the server you're running basted off the Tekkit modpack? If so, it's the mods that are causing problems since Tekkit has over 50 mods, which can lag your computer if you're running a server and client at the same time. I recommend getting a external host (MCProHost, CreeperHost, Beastnode, etc.) to host your server.