"The MX518 and Diamondback top the charts.
Infact (sic)
I was unable to make either of these mice malfunction even at my benchmark top speed of 4.5 m/s. I have put them in at a value of 4.5 m/s for the sake of comparison."
http://www.esreality.com/?a=longpost&id=1265679&page=21
Tried and true non-laser tracking. Combine game settings that can reduce precision with prediction, and pixel-level accuracy can be difficult, and tracking can be jerky/jagged
(only seems to happen with games that are also on consoles, but is still a reason for more DPI), but there aren't odd behaviors to get used to, like with many higher-end laser tracking sensors (*cough* TwinEye). I don't get why snapping/prediction can't be a toggled feature, though.
IME, G5v1 and G500 have negative acceleration if moved too fast at max DPI, but bumping up the weight helps, if you can stand a heavier mouse (heavier -> lower-G physical acceleration to track). Not bad mice at all, but not like upgrades to the MX518, if you're used to and like the MX518. They also don't feel quite the same, like they are wider, though I have not gone and done any measurements.
The MX518 is not a perfect mouse, but managed to get a good enough balance of features, dimensions, and useful performance metrics, to do a good job of satisfying a very large audience, in a way that other mice can't quite do, and it tracks about the same on practically any surface. I know I'm far from alone in having not been able to find a mouse that was an adequate replacement.
Also, "That’s why we’ve integrated the G400 into the same software used to program the G-Series keyboards and the Logitech G13 Advanced Gameboard – so you can create a macro once and use it on either your G-Series keyboard or your G400 Mouse."
http://blog.logitech.com/2011/06/09/introducing-the-logitech-optical-gaming-mouse-g400-2/
I'm not jumping to buy right now, but that has me sold.