I think the problem is either grip (those mice mentioned may differ in shape/weight significantly) or DPI which caused some changes in actual sensitivity.
- In the first case you should either grab the mouse in different way (some mice are, for example, designed for claw grip in particular) or just get used to it.
- If it's about sensitivity only, you can try to get used to it or adjust osu! resolution to your new DPI so it feels the same as when you used previous mouse (e.g. you had 400 dpi and 640x480, now you have 800 dpi so you set higher resolution)
Also, I've no idea if your new mouse was the option you had been thinking about earlier or you just bought it because you needed a mouse immediately, but seems like you switched from shitmouse to mediocre one considering games when you need movement precision.
- Optical>Laser
- Avago ADNS-9800 sensor - It's quite good if you want to play very high dpi, but it still has some positive acceleration issues like ADNS-9500
So, basically - your new mouse's performance is quite good, but if osu!/FPS games were your main "objectives" you could have bought a mouse far better than that one.