You might of seen a few posts from me over the past month or so. I used to build PCs all the time but in the age of ultrabooks and smartphone I haven't messed around with the guts since last decade. This might explain some of the issues I'm having.

I recently purchased a secondhand "HTPC" off Trade Me to hook up to our TV and use for Plex/ Netflix/ BBC iPlayer/ Youtube/ OnDemand

Here are it's specs:

CPU: 3.2Ghz Athlon Duocore (Athlon 64 X2 6400+)
GPU: ATI Radeon 4650 (512meg onboard, 1.5gig shared)
RAM: 4Gig
HDD: 500gig (5400rpm I think)
TVC: Hauppauge TV tuner card

Not earth shattering muscle but theoretically more than enough to act as a Home Theatre PC. Specifically playing Netflix, Youtube, BBC iPlayer and various TV On Demand services. I've also set it up as Plex server/client connecting to our NAS.

It came with a copy of Windows 7 Home Premium (64 bit) and I've done a clean/ minimal install with full updates. I've installed the Catalyst drivers/suite for the Radeon GPU. Other software it's running Chrome, DirectX, Silverlight, .NET, C++, Plex server, Plex HTPC client, and Microsoft Security Essentials.

The bad news is it's performance has been underwhelming - even with ample bandwidth via UnblockUS I'm getting stuttering in Netflix . In Netflix the video starts to stutter, the audio stutters a bit, and then continues as per usual - and then the video catches up to the sound Benny Hill styles. I'm running the video at 720p to try and reduce load. 

I've been using Task Manager and HWMonitor to keep an eye on things and it goes a little something like this for watching Netflix:

The first few minutes the CPU is around 20-30%.
Then it climbs to around 50-60%
Then it starts spiking to 100% every few minutes, which causes the video to stutter.

HWMonitor shows the CPU sitting around 35C when idle, 50C when playing, and close to 70C when spiking/ stuttering. The (stock) CPU fan is working hard and very noisy all the time. These seem like very high temperatures but I've read that the old Athlons run hot.

I tried running Netflix using IE11 instead of Chrome, which gave me a slightly lower CPU load, and more time before the stuttering kicked in.

The machine itself is running really hot - it's a decently airly desktop case yet it becomes hot to touch and even this morning (12 hours after I turned it off) it was still warm. I've got it in a large (3m x 1.5m x 1m) cupboard and am putting some thought into getting better airflow around it.

Yesterday I bought a 80mm case fan, which again has extended the "time to stutter" to an hour or so. But once it starts stuttering there's nothing I can do beyond turning it off and letting it cool down.

I also took the (stock) heatsink off the CPU, cleaned both surfaces, reapplied thermal paste, and reset.

Which brings me to the questions which are doing my head in?

* Is the machine hot because the CPU/GPU are underspecced for what I'm asking them to do?
* or is the CPU overworked because the machine is too hot?

I would of thought in theory the specs are ample for what I'm trying to achieve, but I am completely out of touch with modern specs. My work laptop is an i7 Lenovo X1 Carbon which is a creature of power, speed and beauty - so admittedly I'm a bit spoilt.

If it's a cooling issue then I can fix that with money and time - but how much money and time should I throw at it? It looks like a decent CPU heatsink will set me back around $50.

THE CRUNCH
Having already spent $400 on this I don't want to throw it away. But I don't want to spend money on a better GPU/ CPU heatsink etc. if the base of the machine is under-specced for the job.

Any advice/ thoughts greatly appreciated.