I've been using a 3500 DPI G400 for the past year or two. I never liked the shape, but it seemed like the best sensor I could find with a native 800 DPI step that was still in production. I had been anxious to get a mouse with the same sensor but better shape, so I picked up a Roccat Savu months ago. Immediately after plugging it in, I noticed the sensor felt terrible, even though it was supposed to be the exact same sensor. I could not hit the side of a barn in FPS games with this mouse or in RTS type games like League of Legends (was Gold 2 at the time).
It only took playing with the mouse for a few minutes to figure out it had insanely high smoothing applied to it, so high that I had never encountered any mouse like it before. I used the mouse for less than one day before tossing it in the closet while thinking it was just some Roccat Germans having no idea what they're doing and applying some kind of post process smoothing to the mouse.
Next I picked up a Krait 2013. It uses the same sensor as the 6400 DPI Deathadder 2013. Soon as I plugged the mouse in, I notice it has even worse smoothing/lag than the Roccat Savu. I used this thing for about 2 hours before tossing it in the closet because it was completely unbearable, just like the Savu. Many other people have also posted the exact same feelings about Deathadder 2013 in that the mouse is unbearable to use due to the smoothing/lag. Such a thing does not belong on a gaming mouse period.
Today I just got a Kana V2. I really should have known better by now. The second I plug it in, I notice the exact same smoothing/lag as the Roccat Savu. The two mice feel virtually the same. The problem is obviously the Avago 4000 DPI firmware and it's horrific level of mouse smoothing. Now my Kana V2 is sitting in the mouse graveyard as well.
I've used just about every gaming mouse sensor from the original MLT04, to most everything Avago makes:
I always thought the original Diamondback 3G sensor was the best sensor I've used. The Avago 3090 3500 DPI revision almost as good, but just not quite as snappy. The level of smoothing used on the 3500 DPI ROM is right around the absolute highest you can set, without it being a real hindrance to performance.
The only way the 4000 DPI ROM can be fixed is to release a firmware update with the same or preferably lower amount of smoothing as the 3500 DPI version.
As it stands right now, any mouse that uses this current ROM is useless for anything but an F- grade gamer.