If you are going to limit yourself to using old drivers, then yes you will likely have less overclocking issues.
But by doing so you may be missing out on at least two important points. The first being that older drivers have bugs and some serious issues with current games, etc. And the 56xx drivers you recommend had many issues with my Aopen 5900nu. One particular problem with the 56.72 driver was that it regularly refused to switch in or out of 2D and 3D modes. Caused stuttering and many other associated problems. And although this particular problem may not have much affect on a ASUS 5950u since it doesn't have a 2D mode, the fact that this type of simple but infuriating problem exists indicates that the driver is buggy and therefore is not to be trusted. No matter how many of the 5xxx drivers I tried, for general use I actually kept going back to 53.03 because, apart from known limitations with newer games, it caused the fewest overall issues with my particular card.
Though definitely a valid point, the drivers I mentioned work flawlessly on my ASUS V9980 Ultra. No other driver offers the real world performance that 56.55 or 56.72 offer- I've tested from the 52.xx series up to the latest- and still the 56.55 and 56.72 offer the best performance in games. I used FRAPS to count FPS. I mostly play first person shooters, so those were the main kind of games I tested with. But those drivers also performed best when playing Battle for middle earth, and a handfull of 3rd person titles.
Over all my testing was more limited to the first person genre, but it allows you to draw the conclusion that the 56.55 and 56.72 do offer the best performance.
Those drivers might be buggy, but they have posed NO problem for me thus far, and I have the same card as the author of this thread has. That is why I recommend them. Point in case, if he used ANY driver above 56.72 he'll LOSE 25% or more in performance. Is that worth it to you? I chose no, and stuck with 56.72. I have had ZERO problems with my card. And it is oc'd to 500 core, 975 mem with the AGP voltage at 1.7. Runs fine and respectably cool with the cyclone blower I added on.
As to those drivers not supporting 3DMark05, ok- so? Thank you for pointing that out, but they offer better performance in 3DMark05 than any newer driver. Well, they do on the ASUS 5950U that is. And they DO offer superior performance to newer drivers in the real gaming world. They also have zero stability problems as well. This is with an ASUS 5950U mind you. Other manufacturer's cards might not handle those drivers as well, but the ASUS card loves 'em.
As to what you mention of the ASUS bios, I take your word. Seeing the oc you mention, I just might ditch the ASUS bios. Thank you for pointing this out, I'm sure it'll help with performance as well.
Being that kmanlcn has the same card as I have, the results of my testing would be the same for him and his card. I've gone through a ton of tests with each driver from the stock 52.16 up to the latest drivers. I ran all the 3DMark series with each driver, Aquamark03, and GLExcess, as well as many games with FRAPs- the end result was that 56.72 and 56.55 offer the best performance for the ASUS v9980Ultra. There are no stability issues with these drivers when ran on an ASUS V9980Ultra. Now my results might be different had I used a 5950U from some other manufacturer, but for the ASUS V9980U kmanlcn would be better off using Forceware or the ASUS driver version 56.72.