Keep in mind the 500 will be air and the 600 etc ABC. Try and drive both to compare. The v12 ha shigher maintence and repair costs (plugs, packs etc) and will probably be 22mpg on a run vs 25/26 on the 500.
Definitely smoother though
If not sure, try both.
I did that with my CL600 ... no contest.
Similarly, when I wanted an XK (X100, old shape), I tried both the standard V8 and the supercharged. Chalk and cheese again.
At my (our?) time of life, one of the worst feelings must be "I wish I'd gone for the better* one". You only live once.
*Better meaning faster and more "entertaining", of course.
Mpg for the CL is 23 in normal driving. A light right foot will see 28, but for those journeys I take the Citroen diesel. Lovely wafter and 44-ish.
Whatever you decide, enjoy!