Upgrading CPU options on a older desktop

I just got a older desktop from a friend for only $5 (he was going to scrap it) I am thinking about upgrading the CPU to the Intel Core 2 Quad Q9550 it has the Q9300 in it now I was trying to look online to see if the HP Compaq DC5800 SFF would support the better cpu and I found a few sites that say it will support up to Q9650 while other's that say it's not on the support list. Heck I found a HP site that don't even show the Q9300 as being support while another HP site shows it does. I have already ordered the Q9550 on Ebay for $30
Everything is in working order and I already replaced or upgraded this computer with parts I had laying around the only socket 775 CPU I had was the Q9300 would anyone know if the Q9550 would even work?
Is there any risks for trying to install this CPU besides it not posting if it don't like it?
My plans for this computer was to have a reliable spare computer in case my laptop dies before I can buy a new laptop. I am shocked this computer is already faster then the AMD based A8 laptop that's 4 years newer I'm using now.
Thanks

System spec's
HP Compaq DC5800 SFF
Windows 10
8GB ram
500GB Samsung EVO SSD
Nvidia Geforce 210 1gb
ASUS 24X DVD burner
D-Link PCIe AC1200 wireless

 

You have to look at HP site with either Serial number to confirm it's model and find the service/owner manual and that should tell you what process is compatible with the motherboard. The site doesn't list which specific CPU it uses other then the family names so your going to have to ask HP support what CPU fits on that board and then you will know if it is worth trying.

 

I have the Intel Core 2 Quad Q9300 installed now and it's working great it came out in January 2008 the one I have ordered is the Intel Core 2 Quad Q9550 that also came out the same month. Both the Q9300 and the Q9550 and part of the Yorkfield family of Intel CPU's the HP site shows support up to the Q9300 but nothing higher before I ordered the other CPU I looked into it I found a few sites that said it should work since both are from the same family of CPU's and both came out at the same time. But the best part I found another HP site for the same computer that shows different supported CPU's and that site didn't list the Q9300 as supported. I could order another computer like I have now but newer that shows support for the Q9550 but I rather wait to see if it will post before I pay just over $200 for the tower and ram upgrade.
The one I'm looking at is the HP Compaq 6000 Pro Microtower with DDR3 support and it does show support for the Q9550 and even the Q9650 the one I got now only has DDR2 support. I'm wondering if it's worth buying the newer computer? I know most of the parts in the one I got now will be supported in the newer one besides the ram.

 

What's the link to HP pdf of the motherboard service manual? That is something you have to find to get a accurate info to find which CPU you can upgrade to. Then use wikipedia to search that family CPU line and that will give you more details as to which CPU will fit into the socket. That's how I upgrade my Laptop to Core2Duo. But that one has to do alot of homework here to make sure they are buying the right CPU that will work. And also before doing that upgrade you have to update the BIOS to the latest update to insure it works with latest CPU upgrade as well. Just because the PINs fit doesn't mean it will work.

I did simple search with that CPU you gave and found the family CPU on wikipedia.

https://en.wikipedia.org/wiki/List_of_Intel_Core_2_microprocessors

https://en.wikipedia.org/wiki/Yorkfield#Yorkfield-6M