Speights has been a good-not-great rebounder and viable scoring threat while responding well to the on-court tutelage of post partner Marc Gasol, giving the Grizzlies 9 points and 6.5 rebounds a game in 23 minutes. He's a little bit more of a shot-blocker and defensive presence at the rim than Zach Randolph but obviously nowhere near as good a player.
The biggest tangible difference between the two — beyond Randolph's relentlessness — is where their offense comes from. Though it's a strength for both players, Speights is a somewhat better mid-range shooter than Randolph (making 43% to Randolph's 39% last a season), but is more dependent on it for his offense, taking 43% of his attempts from mid-range compared to 24% for Randolph. And the shift from Randolph's paint-oriented game — 73% of his attempts last season in the paint — to Speights' mid-range-oriented game in the starting lineup has been the biggest drag on the Grizzlies' offense this season.
The one area where they're most similar is that Speights shoots nearly as much relative to his playing time as Randolph, and that quick-trigger approach might actually make the transition back to Randolph smoother because the Grizzlies haven't changed the way they play radically with Randolph out.
Cunningham scores less and isn't the same kind of shot-blocker as Arthur — unlike Arthur, the combo forward Cunningham hasn't been asked to play any small-ball center — but has been surprisingly similar on the boards, actually putting up a better rebound rate than Arthur had last season, with the biggest difference coming on the offensive end.
Cunningham's mid-range shooting has been a minor disappointment so far, getting 52% of his attempts from that area but making only 32%. Comparatively, Arthur was a more effective mid-range shooter a year ago, hitting 41% while taking almost exactly half his attempts from that range. There is hope for improvement here. Cunningham shot 43% from mid-range last season.
Cunningham has been similar to Arthur in terms of getting to the rim, with most of Cunningham's attempts coming in transition, off offensive boards, or on cuts, but a comparative lack of post game has limited Cunningham's ability to get shots in the paint away from the rim.
Like Arthur, Cunningham has provided energy, covers a lot of ground defensively, and makes disruptive plays defending the break, grading out as a big plus defensively.
While Speights has averaged more minutes than Cunningham on the season (23 to 19), I suspect that's about to change with Randolph's return. Randolph's return will eventually move Speights to the bench and into a role as Marc Gasol's primary back-up. No-one else on the Grizzlies' roster — save Rudy Gay — quite duplicates Cunningham's ability to guard stretch fours. And the Grizzlies have been much better — especially on the defensive end — with Cunningham on the floor rather than Speights. My guess is Speights' minutes take a significant hit when Randolph returns but that Cunningham's minutes and role remain relatively stable. It's telling — and reflective of their relative defensive value — that the Grizzlies are increasingly using Cunningham more in the second halves of games.