I used the 4000 for a number of years, but found that it was causing problems in my right shoulder. The reason is the inclusion of a full numpad makes the keyboard so wide that your mouse hand has to sit really far to your right, causing your shoulder to be in a position of constant rotation and eventual strain. I eventually took a hacksaw to it to remove the numpad, which improved things - but it was the main reason I preferred the successor (sculpt) as the numpad is a separate detachable piece. These days I'm a split keyboard ergodox weirdo because it lets me put a trackpad in between the keyboard segments which means my shoulders can stay in a neutral position the whole time
Have you ever tried switching to using your left hand for the mouse. It is generally recommended for ergonomic reasons even if you don't have a keyboard issue. It'll seem weird to your brain at first, but I got used to it pretty quickly, as did everyone I know who has tried.
When I was in grad school (before I had any ergonomic pains), I had my mouse on the left side at work, and the right side at home - so I was using both configurations daily.
I switched to mousing lefty a long time ago. If you want to get up to speed, just play a few games of solitaire or something like that.
Unfortunately, gaming while mousing lefty is often inconvenient. Many games are set up assuming your left hand is on the keyboard. In most cases you can re-bind the keys though.
