The best lens to use for a particular job is one that was designed specifically for the intended format and the magnification range that you intend on using.
A good standard-type lens used within its specified range will give excellent results. A specialized high-magnification lens used significantly outside of its intended magnification range won’t give superior results, possibly not as good as a standard len used within its intended range.
For a projection to fully cover the 30” x 40” print format requires somewhat more than 8.5X magnification of the approximately 95 mm x 120 mm image rectangle recorded on a 4” x 5” negative.
Two lenses that I’m familiar with are the 135 mm f/5.6A and 150 mm f/5.6A EL Nikkor enlarging lenses. These are 6-element 4-group Double Gauss design. They give excellent results in my experience. The 135 mm lens is rated in the Nikon data as having a usable magnification range of 2X – 5X – 10X (minimum – optimum – maximum). The 150 mm is rated at 2X – 4X – 8X. Both will work well for 30” x 40” enlarging, but the 135 mm version is rated up to 10X and so, might be the better choice. It also requires less projection distance than a 150 mm lens.
http://www.galerie-photo.com/manuels/el-nikkor-enlarging-lenses.pdf
I also have a 4/150 APO Rodagon N (2X – 6X – 15X), and 5.6/150 Rodagon G (10X – 20X – 40X). Magnification-wise, the APO Rodagon N is good choice for 30” x 40” prints from a 4” x 5” negative. These are expensive and, now, hard-to-find. The 150 Rodagon G is even scarcer. I don’t think of this as good choice for making a 30” x 40” print from a 4” x 5” negative due to the magnification mismatch.
http://www.prograf.ru/rodenstock/enlarging_en.html
At or slightly above 8.5X I don’t see any real difference in image quality between the EL Nikkors, Rodagon, APO Rodagon N, and Componon-S lenses (I own 135 mm and 150 mm Componon-S lenses). If you want to pay a high price, then the APO Rodagon will satisfy. If you buy it and expect noticeably superior results at 8.5X compared to a standard lens (EL Nikkor, Rodagon, Compnon-S, and so forth) you won’t see it—unless you have a good imagination. The Rodagon G is intended for larger work and isn’t particularly suitable for this magnification.
You said that you already have the 135 mm and 150 mm Componon-S enlarging lenses. These give perfect results. You already own some of finest lenses made for 4” x 5” enlarging.
