Hi mcox,
I have not heard of any issues specific to El Capitan in this regard. However, this
script example will help you to establish the optimum rate when pasting text. What is interesting about your explanation is that you cut the delay in half, but noticed no change in the paste rate.
If using the example script does not improve the issue, we will probably need dtruss output to analyze:
sudo dtruss /Applications/SecureCRT.app/Contents/MacOS/SecureCRT
Please send the output (as an attachment to email) to
support@vandyke.com and reference
"Attn Brenda - Forum Thread #12216".