Here are my opinions, based on a year of ownership.
Quirks & Bugs:
The RT model was new last year, and there were a few issues, but most owners have put on many miles without serious problems. A large number of RTs got tens of thousands of miles put on them, in the first season alone. BRP has been very good at responding to reported quirks, especially the excessive body roll in the 2010 model. They have made some improvements for 2011, and even refined some parts during the 2010 run. I think that is unusually responsive for a manufacturer. The RT is not tried-and-true yet, but it is capable and reliable, for the most part.
Fuel Mileage:
Expect less than 30 with most gas. I averaged 26-28 on my 2010, when not towing a trailer. The 2011 may be better due to improved aerodynamics. This is not a skinny motorcycle, it is a barn door on wheels...do not expect 2-wheeler mileage.
How Far:
The 6.6 US gallon fuel tank holds approximately 6.0 usable gallons, but this puts you on fumes. Expect 100-150 miles per tank of fuel.
Top Speed:
Very difficult to pin this one down. Frankly, I have never tried to top it out. Part of it depends on how high the windshield is raised. Around 95-100 would be a good guess. It will cruise at 80 all day long, with a few beans left over for good measure.
Shake at Highway Speeds:
The RT has a noticeable vibration at 4,000-5,000 rpm. It is also a high rpm motor, especially compared to the Harley or Goldwing. It is pretty good, in my opinion, less than my BMW R1100RT sport tourer, which is not objectionable to me. Vibration is a relative thing, what satisfies me may bother you. Take a test ride or two.
Storage Capacity:
More storage capacity than a Goldwing, even the newest one. Largest capacity on the market...if you compare to a bike. If it isn't enough, there is the (huge) matching trailer.
RT Models:
It sounds like you know the models pretty well already. The BRP Website lists all differences, as does the brochure. The main differences between the RTS and Limited are that the RTS is available in a manual shift and several colors vs. the Limited's electric shift only, and pearl white color. The Limited has a full complement of hard luggage, special markings, and comes with a travel cover...which the 2010 RTS did, but the 2011 does not. I hope I didnt forget anything.
Hope this helps.