May be best for you to go for a bluefin, as you can remove that at any time, so if you do decide to sell it on, you can also sell the handse seperately.
With regards not delcaring it, don't even think about it fella!!! If you have a crash, and the insurance company pick up on it being remapped, (which they will) then your policy is null and void, they will not pay out a penny, even if the crash was not your fault.
Not sure about hte other parts, though have head that fuel consumption does increase slightly!