Sort of hard to equate comfort to 10 percent gains of some performance number. If I'm more comfortable and willing to pay for the change it won't matter if I don't get more performance out of it. However even just a few mm shorter cranks do leave me with at least a sense of less work done for the faster times I have on the same route.
Even if that is just 1% difference, it's worth it to me for a lifetime of cycling. If I was only doing one ride, not so much.