I will try to answer your questions to the best of my ability. The ride quality of the XLR is great. I don't think it can compare to some of the luxury sedans however. It drives like a very comfortable sportscar. The magnetic ride control helped create a very smooth ride along with the rear mounted transmission giving it the 50/50 weight distribution. The Vette is a lot less comfortable overall.
In comparing it to the Benz, Jag, & Lexus, it ranked up there with the benz. In fact I was very unimpressed with the lexus and jag. I would have thought they would have faired better. The Benz was a wonderful car. The one I drove however was $104,000 to be equipped similar to the xlr.
The engine noise was very quiet with the top up. I really didn't notice much during idle or road driving.
The HUD is wonderful. Easy to see with a variety of displays including the speedometer, turn signal indications, audio system, driver gear indicator, and the adaptive cruise control(which is awesome).
Overall build quality again was better than lexus and jag but the benz was high in my opinion. Is it worth the $30000 more? I would pick the xlr.
The interior has a very classy appearance. I saw the shale and the ebony interiors. The shale looked the best I thought.
Acceleration - off the line the xlr can take any of the vehicles I drove. The stats on the xlr are 0-60 in 5.9sec. !!! That beats the competitors without a doubt.
Unfortunately I did not get to try out the voice activation comands and do not have a lsit of them yet. We will be receiving the Neiman Marcus one shortly and I will get the information for you then.
Hope I helped a little.