fhovie,
I have been thinking about what sort of final result you're after on the print. Bearing in mind the first "portrait lens", viz. the Petzval was designed for speed at the expense of everything else, indeed it had a central "sweet spot" but it's not a design criteria at the time, so it's more of a drawback as far as J.M. Petzval was concerned.
If we are going to nail it down, perhaps you are hoping to achieve the kind of look as seen in wet-plate era portraits, where the plane of focus is sharp but has a smooth transition to softness away from it. This, I think, is a special characteristic of Petzval-type lenses; I have two, and still use an original one by Voigtlander produced in about 1863, and to approximate the "look" as intended, I have to shoot at full aperture and through a very strong filter; something like a sharp-cutting blue, but sometimes I cop out and use a No.15 orange instead. The other is a British one by Andrew Ross of shorter focus which I will re-mount for a 6X6 camera.
With modern panchromatic materials, the aberrations of a R-R lens would be perceptable. J.M. Cameron used an R-R lens for her famous portraits which can never be said to be sharp anywhere, even on collodion, but she "modified" the lens by ripping out the stop in the middle which made the lens work at f/8, so as to get more light through but in the process also upset the design of the lens.
For my money, I would really be looking for a Petzval-type lens; as the design was not patented widely many makers produced copies of it, "no-name" examples, or those with less highly-regarded names can still be found at prices far lower than those bearing the more illustrious names such as Voigtlander, Dallmeyer, Ross, etc. Many "magic lantern" projector lenses were made following the Petzval design and they should be quite satisfactory as well.
However, another factor worth considering is that, the Petzval has a very narrow coverage. In order to cover 8"X10" you might need to track down a very large one, and be sure that the camera has enough extension and sheer strength to hold it up. Back then the studio cameras were massively built so that heavy lenses presented no problem at all.
Looking at my notes, for a "boudour" format picture, 4.5" X 7.5" on 5.5" X 8.5" mount, a Voigtlander Series I lens (which is practically a slightly revised Petzval) will need a lens of 15" focal length. The 14" Dallmeyer's Patent Portrait lens, which can be considered as a wide-field variant of the Petzval, can cover whole-plate. So you do the sums.
Good luck!
