You realize you have a transition system! The 2309 is the Core 2 Duo and the 2374 is the iSeries version. Its the same hardware except the CPU’s!
So you also have the [https://ark.intel.com/content/www/us/en/ark/products/42915/intel-core-i5-750-processor-8m-cache-2-66-ghz.html|Core i5 (i750) 2.66 GHz], or [https://ark.intel.com/content/www/us/en/ark/products/41316/intel-core-i7-860-processor-8m-cache-2-80-ghz.html|Core i7 (i860) 2.8 GHz] Either one will give you more bang than the 2.2 GHz Core 2 Duo.
As far as the SSD, you only have a SATA II (3.0 Gb/s) interface in your system so what ever drive you get needs to support this I/O speed, as an example the [https://www.samsung.com/semiconductor/global.semi.static/Samsung_SSD_860_EVO_Data_Sheet_Rev1.pdf|Samsung 860 EVO SSD] offers support as you can see in the spec sheet here “SATA 6 Gbps Interface, compatible with SATA 3 Gbps & 1.5 Gbps interfaces” Make sure the drive you get states it in the spec sheet if not don’t buy it!
Did you say you wanted a 4 TB drive? ;-} There are even bigger drives like 16 GB!
As you can see you have quite a few options here with the Samsung drive. Don’t go too large! Just because you can doesn’t make it a sound investment! Lets say in a year your system dies and you decide to go with a newer system what would you do with your SSD? Get a case for it and use it as a backup drive?
As far as your GPU, while it would be nice to have a more powerful GPU you systems age makes this iffy! All you can get are pulled GPU boards from parted out systems so you could just be getting one that’s well worn. Save your money for your next system.