Will, or should there be a difference in performance, as in effective range, of a radio transmitting in a digital mode vs transmitting in an analog mode ?
Yes, but you'll likely start a fight here with a question like that. It's complex, and some of it is up to personal interpretation.
Analog radios are usually tested at 12dB SINAD.
Digital radios are usually tested at a certain bit error rate.
Since the two don't match up, it's hard to compare, so it usually comes to an opinion. Often the Mean Opinion Score (MOS) is used.
Some will tell you that Analog is -always- better. Some will tell you that digital is always better.
As alcahuete said above, analog gets really scratchy out on the fringes. It's hard to listen to, but our brains/ears can often do a pretty good job of extracting useable info from a garbled message. Usually, but not always.
Digital, on the other hand, will usually decode just fine out to the edges, then there's a brief time where the bit error rate gets high and the audio gets lousy. Then it's just gone.
When the analog gets scratchy and hard to listen to, digital will often come through nice and clear.
In a nutshell my question is will one mode have a better range than the other ?
My experience has been that digital outperforms a bit. Your milage may vary, and as for everyone else, their opinions will vary.