I have a T3500 I just upgraded the CPU to the X5675 6c/12t for email, spreadsheets, misc (after my i7-920 system PSU blew up (I think).. wanting a new personal PC but can't find what I want, and don't want an unsupported DIY build)
I wouldn't even consider trying to use a T3400 for real-time video encoding which is VERY computationally demanding.
I recommend monitoring hardware resource (CPU, GPU, RAM, etc) utilization [for ex. using Task manager’s Performance tab and/or Resource Monitor] to see that your system is being maxed out. Now, if you had enough RAM, an SSD(s), and a GPU with encoding offload (but beware newer GPUs PCIe v3 on tT3400's PCIe v2 motherboard... it works, but potential compatibility issues if not being careful), then maybe a low settings 480p capture? maybe, if you are really good at optimizing the OS and OBS for an underpowered system? just guessing... but unless you had spare parts laying around, it isn't worth spending money on such an old system to only test/play with what will always be a very slow system for real-time video encoding.
for reference, I tried to stream with an Intel i5-6300HQ (2.3GHz 4c/4t circa Fall 2015), 8GB RAM, SATA SSD Win 10 Home edition, Nvidia GeForce GTX 960M and failed as the PC wasn't up to the task (no gaming, just alternating between USB webcam and simple pre-recorded videos, alongside a PPTx slide show window capture, streaming at 720p 30fps with no OBS effects/filters). I'm very knowledgeable about Windows, and the OS was stripped down, fresh build. I’ve learned a lot more about OBS since then, and probably could get it to work now (many month later and daily following this board for a year+), but wasn’t worth it at the time and instead simply got a new PC instead (with an i7-10700K and GTX 1660 Super). Now, there are folks here who got a stream working with lower end equipment than this... but you have to know your stuff.
