Sway bars are great for eliminating the momentary sway induced from a rough road or a passing semi.
You should be able to tow your trailer at freeway speeds under any conditions without a sway bar if your trailer is properly loaded. You should have a minimum of 10% to 14% of the total trailer weight
on your trailer tongue.
I have towed 10,000 lb stock trailers, travel trailers and boat trailers all my life, I'm closer to 70 than 60, without the aid of a sway bar.
Presently I tow my 16' Scamp
without a sway bar on Forest Service dirt roads and freeways. I love Arizona as the trailer speed limit is 70 mph.
I know I'm opening a can of worms when I say, if you NEED sway bar it is a band aid to covering up a serious, life threatening problem.
If it makes your driving more comfortable and worry free by all means use a sway bar, but first make sure you don't NEED it under normal circumstances.