Hey, Quattro, I'm Ray the Hammer. I would like to bring up something about grinders that no one has mentioned... comfort. I am a blacksmith, so I use my grinder more frequently than most people, and prefer a paddle or finger trigger. Grinders with thumb triggers (on the side) get a liitle uncomfortable after a while. Yes they lock, but the lock, which is usually just an indention, wears out pretty fast. All manufacturers make several variations on a theme, so go pick them up and hold,em like you would when working. I have 4", 4.5", and 7" grinders from several manufacturers. I don't have any issues with twist from torque with any of them, but then, I'm a pretty big guy. My girlfriend, however, isn't and she has no problems using any of them.
I use my 4.5" the most, and it seems that I'm able to find more accessories for it than the 4". I also work at The Home Depot, so I see most major brands going out the door at an equal clip.
I hope I've given you a little more insight... if you are going to use this tool a lot and for long stretches, comfort is a huge consideration.