What is the most efficient way to validate messaging with customers?

I think I addressed this above. 

It's vital for you to get objective opinions about your idea. Chances are you've been exposed to your concept for so long that you've lost the ability to be unbiased. Talk to customers! Get feedback from your sales team. Develop regular cadences where you can get that feedback loop with sales, SDRs, and customer success teams.

The short answer here is that surveys are probably the most efficient way to validate messaging with customers. It's quick and inexpensive, and can get you a quick read on how well your messaging resonates. I've even run simple polls on LinkedIn to validate messaging, and it was very fast and effective. 

That said, I would recommend combining the survey-based validation with some interviews where you can peel back the onion a bit and get deeper insights. Ideally, run the interviews first, then further validate using a scaled approach.

I'm a fan of the highlighter test method. We generally will take advantage of being present at an event (know this is challenging in today's environment) and take about 20 copies of two versions of our messaging, then sit down with clients/non-clients and ask them to highlight words that resonate with them, words they don't understand and words that don't resonate with them. Once they go through that exercise, we go back and ask them why they highlighted words in the ways that they did. We then have both qualitative and quantitative feedback on our messaging to use as an input for the next round of messaging. We generally give out small dollar gift cards in exchange for 15 min of their time.

I've answered a similar question in the AMA in response to "Are there ways to test our messaging without spending a dollar on external validation?"

In short, there are three main ways to validate messaging in a B2B setting: 

a) Pilot selling with a select set of sales reps 

b) Customer and prospect feedback interviews 

c) Calls with leading analysts in the space (these are generally part of paid programs)