@Calum Yes @SpookDog runs the Hyperpro fork springs IIRC and is happy with them.
I weigh around 150lbs and to make my '98 DTR a bit better off-road, my suspension setup was:
YSS adjustable rear shock and Lust Racing 25mm jack-up kit (the YSS shock is slightly shorter than OEM and the Lust Racing kit corrects this).
XT600 3AJ fork springs (20% stiffer than stock) and 15W oil (stock is 10W); this is a well-known DTR upgrade for greenlaning etc. and helps the bike jump better and resist bottoming. I adjusted the spring preload/rebound on the YSS shock to suit and the bike jumped better than the 2020 KTM 250EXC I also owned at the time.
I've also heard of people swapping on an XT600E rear shock spring, this apparently sorts the spring rate but the stock DTR shock has no damping adjustment so you might end up with the rear being a bit of a pgo stick (I was running the YSS rebound on position 29 out of 30).
The correct way to set up suspension according to a lot of racers is get the correct spring rate first; this is achieved by aiming for 25% static sag (the amount the suspension compresses when you sit on the stationary bike wearing all your usual riding gear, helmet etc.). If you fall down the hole of just adding heavier and heavier fork oil it will just make the front end feel mushy and unresponsive. Once you've got the right spring rate, then is the time to start working on damping which is a little more subjective as it depends on where you ride, how fast you go, how you like it to feel etc.
I've made this sound a lot more difficult then it is TBH, the spring rate is something you can do without even riding the bike to get a starting point, then a few ride-and-feel sessions and you'll be well on your way.
