ftp. tls

My router is ac87u, firmware 380.67 I use fast pendrive as ftp and ipad in my lan. Speed up from ftp to lan i have up to 35MB / s but when i turn on tls support, the speed drops to 10MB / s and the processor is heavily loaded. My question is, is this normal? Are other routers in this class also...

First of all I'd like to thank you again @RMerlin for the truly awesome work you put in this FW. You can expect a beer or two coming your way. Thanks! I have to say I'm really happy about the latest FW that brought a lot of improvements to RT-AC3200 for me and a lot of others I imagine. I'm...