We've created a nintex 2013 form that has a look up column.
when you type in the first or last name of a user, it takes forever for it to find it.
If you type in the login id or the email address, it is quicker which is reminiscent of 2010.
any suggestions on speeding this up?
Recently my company updated the Nintex Forms 2013 from 2.3.4.0 to 2.4.0.0 while working against Nintex Workflow 2013 3.0.8 and experienced both fast an slow people picker control functionality.
After my analysis, I could show that the people picker control from Nintex Forms 2013 version 2.4.0.0 the following took place.
Scenario 1
On my People and Group list column setting, I do not designate the "Choose From" option to point to a specific SharePoint Group. On the form I observed results being returned when I entered as little as 2-characters in the people picker control. The more characters I typed the faster it sorted down to the person I was seeking.
Scenario 2
On my People and Group list column setting, on the "Choose From" option, I select a specific SharePoint Group. On the form, I observed results where it took at least 5-characters typed before the control would begin to display names to select from. Up until that 5th character entered I would receive a message <<no results>>.
This was very perplexing as the number of people in the group was less than 50 people, and I didn't have any names of team members that were duplicated.
In Nintex Forms 2013 version 2.3.4.0 this was not an issue and it worked pretty well. I recently submitted a ticket and was able to show the support personnel the issue in detail. He sent it to the development team to look into.
Hi
Did you ever get a response about this - we are experiencing similar problems.
v2.7.0.0, same issue 
We were given a hotfix from Nintex support for this issue with the people picker.
The hotfix was a replacement javascript file named "NF.PeoplePickerHelper" to replace the existing file.
It is a javascript file that will replace the existing NF.PeoplePickerHelper.js file under
c:Program FilesCommon FilesMicrosoft SharedWeb SErver Extensions15TemplateLAYOUTSNintexforms
Once you get the file from Nintex Support you'll need to rename the original file and then copy the new .js file to that subdirectory on all servers using Nintex.
thanks 
I have sent it along with other details against my support ticket
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