A question that has been asked often:
What is the difference in performance between the different weighted racquets?
For example 4U vs 3U?
Under Yonex specs: 4U is defined as dry weight between 80 to 84.9g
whereas 3U is defined as dry weight between 85 to 89.9g
There is a 5 grams difference. So what? It's only 5 grams...
For example: my Yonex AT900P 3UG5 and below my AT900P 4UG5
As I have played with both specs for more than a year, I believed I can offer some opinion on the matter.
Using AT900P as an example. This racquet has the sepcs of being head-heavy and stiff.
Head heavy balance is the optimised specs for the overhead stroke like clear and smash. The added weight at the head facilitates the racquet to swing down faster/forceful in a downward stroke like a clear or smash.
The Chinese like to call the head heavy balance as the forehand racquet whereas the head light balance as the backhand racquet.
However, owing to the ease of a downward (pronation), it sacrifices the ease of an upward stroke (supination). Supination is the wrist/arm movement of the backhand swing.
To maneuver well, the supination stroke is important especially in a fast game. For example: a backhand drive, a flick serve, a netkill and the backhand lifts.
(Taking stiffness out of the equation)I can safely say that 4U version is more easy to maneuver and defend. 3U on the other hand is more solid and slightly more power (given equal swing).
The pros of a 4U:Speed, speed and more SPEED (we know speed kills). Also allows one to play with less muscle fatigue.
The cons of a 4U:sacrificing a little bit on power, feel and control (i.e. frame stability)
The pros and cons of a 3U is the inverse of the 4U.
My personal opinion is the 4U performs better than 3U. This is because I play doubles where defence and speed is important. The 4U also makes you less tired if you play in long game or in a tournament. (e.g. in a rubber game stretching to 1 hour)
A singles player will find 3U better since speed is not so important but stability of the racquet head and feel is more important.
The speed of the shuttle in singles and doubles is different. The doubles game is a faster game whereas singles is a slower game. Singles places more emphasis on movement pressure (footwork) whereas doubles is more shot making pressure (quick handling of the racquet).