The K six one tour 90 is great for control. It is also good for people with big serves and volleys. Also the one handed backhand with this racquet feels really smooth. However, there is a new 6.1 tour racquet coming out called the Wilson 6.1 tour BLX. I would wait if I were you for the new BLX's to come out.

I haven't used the Prince Ozone tour, so I cannot say much on that racquet.

The Babolat pure storm GT is a great racquet. Nice buttery feel on swing. Good control. And it has a forgiving headsize. I prefer the limited edition Babolat Pure Storm GT though. I would get this racquet if you cannot handle the K 90, because it still offers great control but is lighter and more forgiving.

Lastly my thoughts on the head microgel prestige mid plus. Sorry, but I have only used the Mid (93 sq in) version of this racquet. The Head Microgel Prestige Mid is really really good. It is not too heavy, has a buttery feel on swing, has good control and is a very stable racquet. I love this racquet. If I didn't love my K prostaff 88, I would definately use this racquet. I think that if you are aound a 4.0 player with a 1 handed backhand you should try this racquet out. I am guessing that the Mid Plus version of this racquet is just as good.

By your racquet choices I am guessing you are a player looking for racquets with good control. I think that the best racquet out of these for a 3.0 -4.5 would be either a Babolat Pure Storm GT Lmtd Ed. or a Head prestige Mid (or midplus)

If you are an advanced player then by all means go for the Federer racquet. This racquet will only make you better.

Really sorry that I can't review the Prince racquet, but I hope this helped!