speaker to big?

I had a pair of Gallo Ref 3.1's in my room, which is similar in size to yours. I could not get rid of boomy bass caused by standing waves. I sold them and bought a pair of Harbeth Compact 7ES-3's. These speakers integrate into my small room much easier than the Gallo's. YMMV...

Two considerations:

Large speakers are usually designed that way to accommodate larger woofers. This may overdrive a smaller room. Also, remember that nearly all speaker cabinets vibrate to some degree, thus they add to the soundfield. The larger the cabinet, the more potential for this.

Second, larger speakers may have drivers spaced further apart and require a more distant listening position to allow them to integrate. Also, in producing more bass, they may need placement further away from the front and side walls, thus requiring a larger room.

It depends on how much importance you place on the presence of deep bass info vs the insertion of an add-on parametric equalizer.

Personally, I would opt for a 'fuller' range floorstanding speaker and lopping the tops off low frequency nodes caused by room dimensions (or necessary set up compromises) than relying on minimizing room problems with small speakers or room treatments for a couple of reasons.
1) Some of the room/bass problems can be well above 60hz, well within the effective response of many 'monitors' and can really muddy up bass response.
2) It is very difficult to treat a room to eliminate or minimize deep bass problems related to room size. Resist buying into all of the hype hear about band aid products. DO some research into acoustics for your self.

FWIW even if you can't set up the speakers that you decide to buy for your room, try to find some of similar size and frequency response and listen for yourself to see if they create any problems (for you, not just in theory).

FWIW.

Quatros will work with most rooms, thanks to its eq which will help you overcome bass problems. It helped me.

You mentioned resolution and imaging. Other variables being constant, a small speaker will image better than a larger one for a variety of reasons based in physics. One reason, for example, is that the smaller speaker will have its drivers closer together. This will give better coherence as the sound radiates from a point that more closely resembles a single point. As a result, the monitor is a little more forgiving in placement than a larger speaker on this point alone. It's small size makes it even more easy to place. Your big speaker may image fine too; however, it may be better if it's moved a bit and you may not have the room for it. Another factor is the potential bass overloading of the room as the posters above have mentioned. If bass isn't controlled, then it will mask other frequencies and you will lose the resolution that you like.

So is your speaker too big? It may or may not be. If the bass is controlled, and if the speaker can be placed properly for imaging, then it's not too big. Otherwise it is toon big. But even despite that, you would get better imaging from a good monitor, but you give up lower octave bass as a trade-off. If so, then add a sub.