I've finally completed my testing of BIOSes with differing 2D/3D memory clocks. Surprising results abound, I'm wondering why I didn't see this in my original testing.
I'm actually typing this post out while using the 450MHz -> 925MHz BIOS, all without any flickering/flashing/screen shakes!
Code:
2D MEM 3D MEM
225MHz 900MHz (1:4) Flicker/Screen shake
225MHz 1000MHz (just testing) Flicker/Screen shake
445MHz 900MHz (less than 1:2) Flicker/Screen shake
450MHz 900MHz (1:2) Works great!
455MHz 900MHz (more than 1:2) Flicker/Screen shake
450MHz 925MHz (just testing) Works great!
500MHz 900MHz (something not so close to the minimum) Works great!
445MHz 1000MHz (seeing if ~450MHz is an absolute minimum) Flicker/Screen shake
450MHz 1000MHz (seeing if ~450MHz is an absolute minimum) Works great!
455MHz 1000MHz (seeing if ~450MHz is an absolute minimum) Flicker/Screen shake
495MHz 1000MHz (less than 1:2) Works great!
500MHz 1000MHz (1:2) Works great!
505MHz 1000MHz (more than 1:2) Works great!
So what does all this mess mean? My thoughts for setting memory speeds in the all-in-one-BIOS are;
1. The HD4870s memory controller likes 450MHz for an underclocked memory speed. Is it a coincidence that it's half of the default speed of 900MHz? Maybe. There could be some technological explanation of why 450MHz works, but the explanation would probably just confuse me anyways. So if you have a stock card with 900MHz memory, or even if it's overclocked to say 925MHz or 1000MHz, you can set your card's BIOS to a 2D memory clock speed of 450MHz, and PowerPlay should function properly without any flickering, flashing, or screen shaking.
2. Values lower than 450MHz will result in the flickering/flashing/screen shake anomaly. Avoid setting your card's BIOS to 2D memory clock speeds lower than 450MHz. Period.
3. Values higher than 450MHz up until a certain point will result in the flickering/flashing/screen shake anomaly. Further testing could find where this point is (IE......it could be around 475MHz), but I'm too tired to do any more BIOS flashing tonight. Since a value of 450MHz is the lowest, and has worked for me with most any 3D memory clock (900,925,1000), there's really no reason to use anything higher than 450MHz. The key is getting the most power savings and heat reduction possible, with an all-in-one-BIOS.
4. The only thing that remains for me, is whether this can be replicated by other users with their HD4870s. While it's nice that this new discovery works for me on my card, it would be even nicer if this was something that is applicable to everyone, and not just a random isolated event.
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I look forward to seeing if anyone can come up with the results I have, as it would finally put a decent close on this whole thread. The end result being a properly functioning all-in-one-BIOS (or working settings) that includes greater (or the greatest possible) power savings and heat reduction over the standard BIOS that usually ships with most HD4870s.