I would go with bookshelf speakers for that size room. Perhaps, if you really crank it you may find their dynamic limits, but I have auditioned over 6 pairs of bookshelf speakers in a room which was 20% larger than yours and max. SPL was not a concern for me. As a reference an average SPL of 90dB with peaks of 95-98 was as loud as I played them to test their ability to pay loud. For me this is an uncomfortable level.
IMHO, the main benefit of bookshelf speakers is that for the same money you are buying better quality speakers. When you go to towers a lot of the cost is going to the cabinet (it is expensive to build a tall cabinet that minimizes resonance) and the money spent on drivers is being spread across more, lesser quality drivers. In your price range, you can get some high quality drivers in a bookshelf speaker. You are sacrificing the tower's ultimate SPL and bass for a higher level of sound quality. If you add a sub, the issue of bass is resolved.
I am not familiar with many of the speakers you have available (assuming you are in Europe). It is obvious that zieglj01 has a good awareness of this, and I know he has listened to many more speakers than I have so he can give good direction.
However, while I think someone has already mentioned it, KEF makes a good speaker.
Take your time and be as thorough as you can selecting your speakers. They are the biggest determining factor of the sound quality of your system.
The audible difference between speakers is dramatic and generally easy to distinguish.
Audible differences between amps, CD players, DAC's and other digital and/or electronic components is an on-going debate (in other words, it is so minor there is some uncertainty whether the difference exists).