renice to favor chrome over deluge

I had soso results.

I reniced chrome to -20 and xorg to -20 and deluge to 20.

Deluge writes to a usb external drive zfs.

My goal is to have fast snappy web surfing and youtube video playing while deluge does its thing in background and always subservient to web browser.

Chrome seemed to churn and chug. Not sure if it was good move.
Next day with nothing reniced things seemed better.

chrome is in general fast but youtube movies slow it down a bit esp when I am playing more than 1.

I have zfs on the external drive where deluge writes and I noticed deluge makes arc go big.

There are about 400M swapped and ram is 16g total on 6 core amd64.
zfs arc seems to fight deluge python a bit and thing slow down sometimes.
I think this is because stuff is being swapped.