Rendering with Arnold. Should I get a eGPU?
There are 27 different 12th gen i7 processors. If you could provide specifically which one you have it might help. GPU rendering can definitely be faster than a CPU but GPUs can't perform every function. You'd want to find a list of functionality for Arnold to see if your file has anything it in that GPU can't render.
Unfortunately, 3d work is one of those tasks that works a computer harder than any other thing you can do on a computer. So, cheaper and lower end hardware, GPU cards and processors cripple the whole experience. To do 3d work in a speedier and frustration-free way you kind of have to spend some money. It's just the nature of the beast. And if you have better hardware, Max can run very, very well and without frustration.
So, you are in-between a "rock and a hard place." You want speed but to get speed you have to spend money. You have no budget so you likely won't get speed. You aren't alone. There are 1000s of people who try to run Max on average or below average laptops and most of them have disappointing experiences.
Now, one thing you might consider is using a Render Farm to render your project. They are pretty affordable these days. I use Rebusfarm but there are many others. But, you say your frames take 30-45 minutes to render so it sounds like a heavy file. So a Render Farm might get pricy as well but it's worth a try. Most of them offer free points so you can test a few frames and calculate how much a full project render might cost.
Another alternative is to carefully inspect your file and try to optimize it so it renders faster. You don't give any details but find what consumes the most time and try to optimize. Reduce face count, reduce particle effects, reduce, reduce, reduce. Yes, that takes a lot of time, but if faced with no alternatives budget or hardware-wise, sometimes you need to bite the bullet and spend hours optimizing so you can get the job done. I've been down that road many times in my earlier days before I embraced the hard and cold fact that I had to spend a lot of money to get Max's speed that it's capable of.
So to circle back around to your original question, will an adapter and a GTX 980 render faster than your i7 CPU, most certainly I'd say. Especially if Arnold has a Hybrid Render functionality like V-Ray does where both the CPU and GPU render the same frame. On my machine a Hybrid Render is scary fast. You'd likely see some speed as well but it's hard to know. And only you can determine if spending the $700 or a GPU and a few hundred on and adapter was worth the investment. If it now makes the render take 15-30 minutes instead, it will still take many, many days to render 90s of animation even if it was 24fps. That's 2160 frames times 15-minutes or 540 hours (22.5 days).
My advice would be to optimize the file significantly or use a Render Farm. You don't say if you are a student or if this is a professional job. If professional, most clients will understand if you tell them they need to pay for the render. Then you can pay for the render farm. If you are a student, it's harder, but I'd bet most professors realize you work with slower hardware and would understand if you trimmed your project back a bit so you can get some render times you can live with or afford.
Good luck and maybe post back if you go the GPU route and are pleased. That will help others and students in your situation.
Rob Holmes
3ds Max (2023-2025), V-Ray 6.2, Ryzen 9 3950-X Processor, DDR 4 128MB, Gigabyte Aorus X570 Master motherboard, Sabrent Rocket NVMe 4.0 M.2 drives, NVidia RTX 4090, Space Pilot Pro, Windows 11 Pro x64, Tri-Monitor, Cintiq 13HD, Windows 11 x64
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I agree - why not submit your render job to one of the many commercial render farms, at a fraction of the cost for an external GPU? All you need is a reasonably fast Internet connection for the upload.
And the costs can be immediately be tax deducted if that is relevant for you...
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I would love to see this scene - 45 minutes for one frame is a crazy long render time. I think there's a lot that could be done to optimize the scene.
I don't know how familiar you are with max/arnold, but take a look at your samples and make sure you're only sampling for what you need; there's a very distinct point of diminishing returns when increasaing the samples. Also remember that "Camera (AA)" samples is like a multiplier for all the samples under it, so be careful cranking that one.
Also consider your target resolution. Do you need to render in 4k? Rendering in 1080 would take 1/4 of the time...
