I play with the Organix 8 - and I am very pleased with it.
The Organix 7 has a slightly larger headsize so a bigger sweetspot and more power. The X8 will have a little more control, little less power.
With the Volkl's - the larger the number (e.g.: X7, X8, X9, X10...), the more of a player's racquet. Which means smaller headsize (usually), maybe heavier, less power, more control
So start with the X7, highly recommend the X8 and try moving around the spectrum.
... that said, you should demo the top tweaners... Head Youtek IG, Babolat AeroPro, Dunlop Biometric 600, Wilson Steam 100 BLX, I used to use the Prince Ex03 RED but found the X8 has much more control and feel, but it is a good racquet...
However, I am very very happy with my X8 - wouldn't trade it for anything. I tried all the above and none of them worked for me as well as the X8 (The X7 wasn't available for me to try at that time).
keep in mind this is 100% subjective and varies from player to player...
... and THEN, you can start messing around with strings!