First of all the Boberg is more than just different.
It has a longer barrel length that the R-9 and at these shorter barrel lengths - that is significant.
There seem to be endless posts on this forum about "which ammo is best in my R-9?" And "Is the 115gr better than the 124gr?" And when you go out and look at the test data - you can't even find people who test out of a 3" or less than 3" barrell. So you sort of have to think - if you come across a test with a 3.4" barrel and it's at a certain velocity with certain penetration and expansion characteristics, you're going to get less impressive performance out of that round from a 2.9" barrel. I'm just saying that the difference between a 3.35" barrel and a 2.9" barrel is significant - the difference between Boberg's design and the R-9 is not just cosmetic. A longer barrel in an overall smaller profile - if it functions, is superior.
The second thing is, if you look at the ballistics tests, the differences between standard and +P loads is significant. If we just stay with the Gold Dot which the Rohrbaugh seems to love so much...
Speer 9mm 124 grain Gold Dot JHP +P:
3.4" barrel 1155 fps, penetration - 13.2" expansion - 0.62"
Speer 9mm 124 grain Gold Dot JHP:
3.4" barrel 1068 fps, penetration - 12.6" expansion - 0.59"
So the ability to fire +P ammon is significant even within the same brand of ammo.
Another point is that there are just a whole lot of bullets that the Boberg would be able to fire that the Rohrbaugh cannot. I think that's significant also.
Keeping in mind that Rohrbaugh has already come up with a functioning gun that is in production and has made it to the hands of consumers.
In some ways I feel this thread is not fair to Rohrbaugh... I mean almost everything we say about the Xr9s is hypothetical... If it does this if it does that that, if it feeds reliably, etc, etc...
But in the context of what was asked in the OP... if the Boberg makes it out of the factory, barring quality issues, I think it's not just different, it will be better.
