Can I install a SSD of >= 256 GB on my Dell Optiplex 790 (Minitower)?

I have a Dell Optiplex 790 Minitower desktop computer. I am planning to upgrade to SSD.

Currently I have two 512GB Hard Disk Drive connected to my machine (via SATA0 and SATA1) and an Optical Drive (via SATA2).

I contacted Dell and asked whether I can upgrade to 256GB SSD or not, for which they said my machine supports maximum of 128GB SSD that they found through Dell manual (according to them) and also state that my machine has maximum SATA for 3Gbps (meaning it do not have SATA III). Later I searched for the Dell manual for my machine and found a Technical Guidebook where it is stated that I have one SATA III and 3 SATA II as shown below (Figure 1.0). But about the 128GB SSD, they were right. It is stated that my machine can support 128GB SSD and this is where I need help as 128GB SSD is not enough for me as I have to use some heavy application which requires a quite large storage (not for gaming).

Figure 1.0: Page #14 from optiplex-790-tech-guide.pdf

Furthermore, I have seen some YouTube videos where they installed 256GB SSD on some other model of Optiplex 790 (click here).

To further investigate I used an application HWiNFO where it shows that my two existing HDDs are in port that provides 6Gbps but one of them is running at 3Gbps (which I wonder why?) as shown in the below picture (Figure 2.0). But the Dell Technical Manual I am talking about, I did not find anywhere mentioning the Gbps (Figure 3.0).

Figure 2.0: HWiNFO result summary for my Optiplex 790 Minitower

Figure 3.0: Page #04 from optiplex-790-tech-guide.pdf

Additionally, the below is the SATA ports on my machine’s motherboard (Figure 4.0).

Figure 4.0: Sata ports on Dell motherboard 0HY9JP.

To conclude, I want to use my existing two HDDs (500GB each) one will be connected to SATA1 and the other will be connected to either SATA2 or SATA3 (where optical drive is connected) and I want to install the new SSD on SATA0 (beccause probably it has the highest speed amongst all). Hence, can I install a 256GB SSD or 512GB SSD on my machine safely and will I get all the benefits of the SSD’s speed (6Gbps) along with the two existing HDD (please note that I am okay if I have to disconnect/ sacrifice one HDD for safety and speed)?

Dell Documents:

• Dell Optiplex 790 Technical Guidebook

• Dell Optiplex 790 Custom Brochure

Edits

After further research, I found here that Dell themselve is selling upto 1TB SSD for Optiplex 790 (Figure 5.0).

Figure 5.0: Optiplex 790 Parts & Upgrades for SSD from Dell website