Store showrooms are a great idea but it just never works out that you can get any confidence when comparing quality sets. Even the most knowledgeable and discriminating people will punt to a large degree on the showroom experience. The lighting is so far removed from normal and the sets get messed with all day long to the point that even if a store did take the trouble to set them up they are no doubt all screwed very quickly.
I would understand everything about the technologies, match it to your environment and viewing habits, see what sets most people at home theater sites are buying and then get a good feel for what the knowledgeable people (hobbiests, techs, etc..) like and dislike about the models. Some good forums are www.avsforum.com (stop by the gaming forum too), www.hometheaterspot.com, www.hometheaterforum.com etc...Just like here, read, search, post and take opinions with a grain of salt. I think that you should be able to narrow down your choices and get a good amount of confidence in your decision.
Once you are ready, go to a store and check them out. I would bring a few good DVDs (some bright and some with good black levels - Finding Nemo/Matrix) and a basic calibration disc like Avia/DVE. Set it up with the user menu and check it out. Spend some time watching - it's easier at a high-end store than a big box store. Make sure you are happy with what you see and don't get any major issues like the DLP rainbow or LCD screendoor. For the most part it's going to be really hard to simulate home lighting and viewing environment but if you are going to spend this kind of money you might as well go and kick the tires before you take it to the test track. It may save your from an obvious issue.
I can't stress enough the advantage of dealing with a local dealer who will let you audition and swap the set out if you don't like it. The true test is getting it in your home and doing some serious watching under normal lighting and viewing conditions (many a loved store set is quickly hated at home despite the best of beginnings). There is nothing worse than getting a great deal on a TV over the net thinking you can live with any issues and ending up taking a bath on it 6 months later when you can't live with the issues anymore (it happens).
As far as your room, I don't think there are any inherent limitations other than it possibly being too bright for a front projector (not an issue for you). I would really keep CRT based RPTVs in the mix as a back burner default just in case. A lot of people have gone looking for the new technologies and ended up feeling that they were going to get the best picture regardless of price with a CRT (I was one a year ago - I just didn't get the wow). It may not be cool but with even moderate attention to proper settings you can get a jaw dropping picture that is big and cheap (Porsche picture for a Ford price). It's at least worth using as a reference point anyway as I have yet to meet a dedicated video enthusiast who honestly thinks that the CRT picture quality can be beaten by today's alternate technologies under ideal viewing conditions.
That's the best of my advice. At the end of the day it's going to be your money and your happiness so hopefully that helps you maximize both and sends you to the right places to research. Good luck and make sure you update as you work through the process.
BTW - Onix Rockets can be found here:
http://www.av123.com/ I don't own this set but a lot of fairly well respected people at avsforum and other sites love them. The sub has also been very well reviewed although it is stronger in musical accurasy than deep earth shattering rumble but you could always grab a different sub depending upon your preference. They would certainly be on my list to audition. You might find someone in your area that will let you come over for a listen.