Given budget restrictions, personally, i don't have exactly what i wanted but i am currently satisfied with the setup.
Mouse; i change a bit the DPI settings whether i'm in a game or just browsing and working. For games, any game, i set mouse DPI to it's max, 2400DPI on current mouse, and adjust the response and sensitivity ingame to fit to what i am used to since i began gaming with a mouse (with the original Quake with a ball mouse xD ). Only exceptions to these settings for games are games like Civilization were i don't need such a fast mouse and response for those turn based games.
For browsing and work DPI goes down to 800 but the travel distance of the mouse in both gaming and browsing is similar, about 5cm (almost 2 inches) for a 360º turn and about 4cm (a little over 1,5 inches) to go from one side of my screen to the other (1920x1080p 22,5").
As a rule of thumb for games i use max DPI available so movement is more well defined, especially in FPS's. The more granular the setting the better, imo ofc.
To answer your question of "what is the perfect mouse" personally i got to have 7 buttons minimum and good/high DPI (above 2000) for games and also very smooth pads, not rubbery. The feel on the palm of the hand is also very important and how high the wrist elevates to encompass all the buttons with the fingers. Good wrist support is a must for long time gamers, like me.
Sound is to me very important for my games, whether a FPS, RPG or TBS i need to feel immersed in it and the sound quality is a very important part and if one can have a 360º surround even better. At this moment i don't have all i wan't (budget limitations) but i have what i think essential. Currently only using a 5.1 Headset, real 5.1 not software emulated, connected to my mobo 5.1 output whether i'm gaming or working. Objective will be to get a 5.1/7.1 sound card and equivalent speakers for work/browsing/movies and keep the headset as is for gaming only.
IMO headsets need to be over the ear to enclose outside noises and minimize sound leak from the headsets themselves, not to heavy (although my current ones are pretty heavy but the foam pad makes up for it's weight), sturdy to take some falls and tugs without breaking, good and long braided cable (bluetooth/wifi/radio suffer from delays sometimes, not good when playing FPS or action intense games), golden connectors/jack's and a clip-on "controller" to change sound and other settings on the fly somewhere along the cable, near the user's chest or waist, soft and breathable pads over the ear to avoid perspiration and, to finish with the obvious, a large dynamic range. Microphone isn't obligatory but i usually buy headsets with one that i can detach if i want.
Think that's all.... for now ^_^