i just found your site today, your tips’n tricks are very interesting.
I’d like to share my experience of render settings with vray.

Here are my ways for rendering faster when woking on image with vray :
- as you said, decrease rendering size (320×240 or 480×360)
- i don’t like using override mtl because i can’t see the “bleed” or “bounces” of material colors, but not loading maps is very fast !
- in global switches tab uncheck displacement, in reflection/refraction i use max depth to 2
- for the image sampler, i stay with adaptive subdiv set to -1/2 (default), also renders are even faster with fixed (no img sampler)
- for the antialias, i don’t use any antialias (unchecked), or i use “catmull-rom” which is faster than “area” (“area” takes few more little seconds to smooth the render, and i like “catmull’rom” sharpeness)
- for the GI, i use several methods for fast renders, it depends :
1) – Primary & secondary bounces set to light cache with a value to 250
2) – PrimBounce = IrrMap : preset “very low” + HSph. subdivs decreased to 30 + unckecked multipass, SecondBounce = LCache (250)
- in “Settings” tab, DMC sampler : as you said, increase adaptive amount from 0.85 to 1.0 + increase Noise threshold to 0.05 + decrease global subdivs mult to 0.5 or 0.8

After all that stuff, image render is faster but quality is far away and we have to know that many details are not visible…. details that we will have to handle with a high render.
I’m using render region with good quality presets to see details, and go back to low quality presets for global img.

First monthes i used vray, i spent many times playing with settings, trying to get renders done in time. Sometimes that was painfull, but that helped me learning vray (i’m still far from a vray master !).

Now, in my production flow, i use two plugin/scripts that really help me focus on the image/subject instead of spending times with render settings :
1) – “Vray Quick-render” from author Alex Kramer (aka “Track”), which can be found in his free scripts package “TrackScripts“, this one is very handy for changing settings into low, mid and hi presets only in renders (not in scene), so your final presets stay unchanged
2) – “Solid Rocks”, this one is not free but really, really cheap regarding render time saving. I don’t use it when working on my scene, but only when rendering final high big images in big resolution (at least 3000×4000) with big quality. I have to render several times (2 or 4x) my final image beacause my clients change their goals, deadlines are very short… that’s why i’m using it. I don’t want to say “this plugin is the solution” NOOOO ! but it makes mathematical interpretations of your scene depending on the render size and gives you settings that are really optimized. The goal is to avoid unnecessary high presets.

I totally agree with you when you say “keep the control”, and i still play with settings, but deadlines are short …. so here is my workflow to speed up calculating and see results and focus my brain on client desires.

I also have to mention the materials handling :
- avoid unnecessary glossy (as you said)
- keep an eye on subdivs (don’t keep a value higher than 6-8 for an object material lost in the background of your img !)
- vray seems to be afraid of opacity (i found it time consumming)
- try to convert standard materials to vray mtl as many as possible (i use another script “VrayMtl Converter v2.5″ from 3DZver in scriptspot

Hope that helps, cheers