Hello Freida,
I'm glad you're having fun on your new iMac. And....no issues!
I would plump for the 5700 to 'balance' your system (seems like you're leaning that way..?) 50% speed difference for a few hundred is worth it. That's half a gpu better! It also future proofs your investment. Considering you're a Vfx artist.
There's nothing wrong with the 5500. Anyone coming from 2017 or 2012 (me...ME!) will notice a warp drive difference.
HD with super high frames. QHD with high frames. And both in Ultra mode. Some 4k gaming, depending on age of game. (I found WoW np in 4k.). 5k. Fans on max settings. WoW setting '5' at 5k 93 fps. Now that's pretty impressive for WoW. For any old game it's pretty gluttonous on resources. If you're a part time gamer/'light' gamer. I would have thought the 5700 with it's 8 gigs should be 'good' for at least a couple of years.
The XT has that bit extra performance... (which for those that need it...will know who they are...) but it's that 16 gig of VRAM which is the killer feature there... In, eg. 4k gaming. That might be noticeable in some games. And the 'latest' games over the next two years are going to keep pushing texture size/amounts. Game sizes are getting huge. And that's with the increased poly size, bigger landscapes...and mainly, the textures to go on more complex scenes.
In creative workflows. You have some people who need 64 gigs of system ram for their army of plug ins. They know who they are.
Similarly. 16 gigs of Vram. 50% more Vram than the 5700 vanilla. And that's partly what you're paying the premium for. And 10% or higher difference in speed. It's always about buying 'seconds' for £££.
It's about texture size. In games. And in creation software. I was running XSi (Softimage...) on my Athlon 800 MHz and Nvidia gpu. And the one thing that choked things real quick (back then) was memory. Holding a street scene (even with simple boxes...for models...) with lots of textures put a real strain on the rig I had back then. Modest by today's standards or even my old iMac. But it stuck with me. System Ram. Vram. So I thought I'd always buy the most Vram I could (and yes, a big dollop of system RAM.). 32:16 on my current rig.
Things are different now. An experience fx artist like yourself will firstly know how to be economic with luxurious resources. But the gpu workflow is increasingly gpu based. So having the grunt of a 5700 makes complete sense. The lack of such a powerful option before in an iMac has been vocally lamented by myself and others.
This iMac should be more than enough to paint 2D, paint in 3D, render in 3D. Model with millions of polys. That 5700 8 gig is going to kick az. Best thing to do would be to test texture painting on 3d models or a scene with lots of 4k texture sizes and see how the 5500 handles it. Then imagine 50% MOAR! The 5700 with 8 gigs makes more sense for you, from what you've said. So if you were once talking about an iMac Pro for your budget...pushing to the 5700 and you'll have an iMac Pro like experience for up to £2000-ish less.
I want to tell you to get the 5700XT with 16 gigs of Vram. But only you'll know if you need that as a VFX artist who may or may not take work home. Me? I'm thinking of scenes with lots of textures and where games or creative software might be in two+ years time. I remember thinking 8 gigs was 'a lot' and now game reviews sniff at 4 gigs of Vram.
Even my 680MX could handle Z-Brush with a few hundred thousand poly models. I'm going to bench my new rig with Z-Brush and see what detail levels I can get in real time and then render.
From what I saw of Maya 'back when' it seemed to run 'slow' with even modest scenes. I would have thought now, 32 gigs of system ram, an 8 gig gpu and an 8 core it would be far more tolerable. But my knowledge with Maya is not upto date. I'd be curious to hear of how you find the rendering of scenes...and how the iMac handles 3d scenes in the modelling window. If you're under NDA
then speak in general terms, ofc.
I'll download the latest Blender and run some test renders.
Azrael.