I would say mindreads should be first, then combat, then completing quests. Going into XP debt means it takes longer to level, so you can get an XP bonus from combat (with higher level opponents) slightly longer.

With David, I didn't find his gloves to be that great. If you just suggest that you are planning to turn him in a couple times, you can get him to run away, and then later meet him to the far south west in Broken Valley (mountain path to the fjords), at which point he can be mindread for a stat point.

Linda's purse is only in the church after mindreading.

If you refuse Richard's second quest, he will head to the farm himself; going there and siding with Lomaxm, in the conversation with him afterwards (assuming he survives), you can mindread for a stat point. The quest experience early may be of more benefit, since this would need to be delayed until most of Broken Valley has been explored, so you can turn in all found goblin hearts.



Quoting myself from the topic Who's playing DKS on nightmare difficulty ?:

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Before defeating Zandalor I was level 37.47. In D2:ED I finished at level 36.75. At least part of the difference was due to balancing changes in DKS. For example, in D2:ED I got to level 18 in the fjords before heading to Sentinel Island, while in DKS I made it to level 22. The difference in experience on those two levels from mindreading the island was still only 11.7% of the experience needed to reach level 38. There was also additional experience from quests in DKS, though not a lot (I never tried to figure out how much), according to a Larian comment on quest experience balancing to make it easier to level at the start of the game.

In D2:ED I delayed turning in some quests, but didn't really go out of my way trying to level. I used the Talisman of the North for quite awhile, and between about level 13 and the Hall of Echoes got Wisdom up to level 9 or 10, 4 or 5 of which was from equipment bonuses (equipping Rothman's Bow to turn in quests). Before the Hall of Echoes I boosted it to level 13, to see if I could get to level 37 before the end of the game, thinking the area might be larger than it was. I reloaded for some useless mindreads, but not all.

In DKS I specifically tried to do all the mindreads first, then clear opponents as much as possible and then turn in quests, to maximize the experience given. I didn't learn Wisdom, though did eventually collect jewellery with a combined +8 bonus. I deliberately mindread pretty much everyone.

Neglecting the balancing and island mindread differences between D2:ED and DKS, at best (assuming only a modest increase in quest and opponent experience levels) my efforts brought me from level 36 and 3/4 to 37 and 1/3.
It seems there is a slight benefit trying to maximize experience, but not enough to worry about if you need to turn in quests early to level, or simply wish to do side quests as you get them, etc. If I wanted a more exact idea of the difference I'd play again doing side quests as early as possible; I can't see that happening for my next character, but I will not be as strict about delaying quests.