Doing that for brexit would have made it +6% off actual results, 2014 was 4 Pts off actual results and 2012 was a bit over 3 Pts off. Polls were off even more in 96 (not winner though) and 80. IBD has constantly been accurate on presidential elections and I believe 538 rated them most accurate in each of the last three.
For the current election cycle, 538 has analyzed 17 polls from IBD/TIPP and they have given that pollster an A minus rating. They have an average error rate of 2.3, they have called 78% of races correctly and they have shown a 0.7% Republican bias. All those scores are excellent.
http://projects.fivethirtyeight.com/pollster-ratings/
By way of contrast, Selzer & Company has a A plus rating. 37 polls analyzed, simple average error 4.6, 84% of races called correctly and 0.0 partisan bias.
Selzer is currently polling for Bloomberg News and they have the race with Clinton up by 9 in the 4-way.
http://www.bloomberg.com/politics/articles/2016-10-19/national-poll