At those sizes the enlarger alignment is super critical. The alignment, the quality of the light, the condenser's performance at distributing light evenly, the stability... And then there is the dodging and burning, the filtering techniques, filter choices and so on. There are so many variables that in the end, you might be just fine with any high-quality lens. At that level, each little step is worth 1% and the Apo-Nikkor itself will only add 1% in quality.

These days I'm printing 16x20 FB prints. About 20 Prints per 5 hours session. From those 20 prints, I usually lose about 5 due to dry-down and overall unsatisfactory look (I want perfection). Everything plays a role for the perfect print: Even your mood while printing plays a bigger role then the enlarging lens. If you're somewhat tired while printing, believe me, you can end up throwing all your valuable prints in the garbage for having printed on a wrong Contrast filter the whole time. Even half a value can contribute to unsatisfactory results.

If I was you, I'd put a lot of time in building skills and on a great Focomat Ic enlarger, first.

By the waym where do you plan on getting 40" paper??