You should not notice any loss of website performance with 4000-6000 lines of .htaccess code.
This quoted statement below made on the Apache website is typically misunderstood/misinterpreted. There is a performance hit in milliseconds when AllowOverride is used in the httpd.conf Server config file. If your site is using .htaccess files in every single directory/folder then you will experience another performance hit in milliseconds, BUT if you only have a small number/finite number of .htaccess files such as an htaccess file in your Root folder and an htaccess file in your wp-admin file and a few more .htaccess files here and there then any performance hit that does occur is going to be very insignificant/not noticeable/milliseconds.
The first of these is performance. When AllowOverride is set to allow the use of .htaccess files, httpd will look in every directory for .htaccess files. Thus, permitting .htaccess files causes a performance hit, whether or not you actually even use them! Also, the .htaccess file is loaded every time a document is requested.
And of course .htaccess code can be used to increase website performance/load speed. Example: W3TC uses .htaccess code to boost website performance/website speed. ;)