I found five relevant studies dating back to 2009. Taking the oldest first:
Silverpop International Email Marketing Benchmark Study, 2009
This one doesn’t break out results by mailer type, so it’s probably dominated by business-to- consumer marketers. But it does distinguish gross opens from unique opens, which are significantly different. It also shows median as well as average results, in addition to top and bottom quartiles. This is a good reminder that there's a very substantial range of variation in different marketers' performance. The difference between the medians and averages is also something to bear in mind when looking at the other surveys, which only report averages.
Silverpop is also the only study to give both bounce and unsubscribe rates – the others give one or the other.
Here is the U.S. data from the Silverpop report.
MailerMailer Email Marketing Metrics Report, 2011
I just discovered this one and am impressed. It goes beyond simple reporting to analyze the impact of delivery day and time, number of links, subject line length, and personalization (some surprises here). The repoort breaks out results for several categories, of which the most relevant are probably Computer, Consulting, Large Business and Small Business. (I’ve added a simple average to use later.)
In general, this study shows substantially lower open rates than other studies, somewhat higher click rates, and higher bounce rates. I’ve calculated the click-to-open rate, which isn’t necessarily the result you’d get if you looked at the actual average. But it’s worth having as a point of reference.
Here’s some detail from the study itself (you'll have to click on this to make it legible). The business categories account for two of the four highest open rates and are all in top half of the click rates.
Eloqua Marketing Metrics Outlook 2011
You’d expect Eloqua to put out a good study on this topic, and they deliver. The best-in-class, average, and laggard classifications illustrate the huge gap between even average performers and best-in-class. They also reinforce the point, illustrated in the Silverpop data, that medians are significantly below averages because of high-end outliers. Not to go all stat-geeky on you, but that really matters if you're looking for a benchmark that reflects "typical" performance.
Arguably all Eloqua clients would be relevant to marketing automation users, but the most relevant for true B2B would include Manufacturing, High Tech, and Business Services:
Across all categories, Manufacturing has the highest open rate and is tied for second highest click-through, but the two other "true" B2B categories rank at the bottom. The combined averages for the three are just slightly below the average for all categories.
Epsilon Email Trends and Benchmarks Q42011
Epsilon is another industry stalwart, publishing regular quarterly reports. But they only provide one category for B2B Products and Services, plus another for Business Publishing. The open rate for that category seems pretty high compared with other studies, although the click rate is largely in line.
Signup.to The UK Email Marketing Benchmark Report 2012
Finally, we have a study from Signup.to in the UK. I’d question its relevance to the U.S. market, but the 2009 Silverpop study showed similar figures for both. It includes figures for B2B Sales, B2B Service, Industrial/Manufacturing, and IT. These vary pretty widely, especially for open rates.
Compared with other categories, the business emails get somewhat above-average response:
What Does It All Mean?
Within each report, open and click rates B2B categories tend to be in the middle or above average. But the over-all ranges vary substantially from one report to another: at the extremes, MailerMailer open rates range from 7.1% to 17.6%, while Epsilon ranges from 14.2% to 35.6%. Without understanding the reasons for these variations, it's hard to select a single reference point as a benchmark. The best I can suggest is to throw out the outliers, which would leave Eloqua and Signup.to. I'd also tend to favor the Eloqua figures because they are based on the "average" performers, and therefore are closer to a median rate. (You'll remember that averages tend to be higher than medians, because a handful of very high performers distort the results).
That said, the table below shows the average figures for each survey (which, you'll remember, themselves hide significant variations within each report). I’ve calculated an average of averages, excluding Silverpop since it didn’t break out B2B from B2C. As it happens, the averages fall somewhere between the Signup.to and Eloqua figures. So, if you forced me to propose benchmarks for B2B email performance, I'd say those numbers are as good as any.