Eric Davis has the best two year Power-Speed# and it is by a wide margin

Here is the definition Power-Speed# from Baseball Reference:

"2 x (Home Runs x Stolen Bases)/(Stolen Bases + Home Runs). The harmonic mean of HR and SB. To do well you need a lot of both. Developed by Bill James."

Here are the top 3 single seasons:

Alex Rodriguez	43.91	1998
Alfonso Soriano	43.36	2006
Eric Davis	42.53	1987

AROD is first but his edge over the next guy is not very large. But as we will see in the first table below, Eric Davis has a large lead over the next best two year period. In fact, there are only two cases that are within 10 and none within 5. 

To find the best cases, I used Stathead to call up all the cases of players getting 50+ HRs and 50+ SBs over a two year period starting at ages 20-21 up to 32-33 (Power-Speed# is not one of their searchable stats so it has to be calculated from HRs & SBs). There were no cases before or beyond that. The 50-50 cutoff should be enough to find the best seasons. 

The table below shows the highest PS#s for each age group. It also includes the second highest for ages 24-25 to see how close that was to Eric Davis.

Age	Player	HR	SB	PS#
20-21	Mike Trout	57	82	67.25
21-22	Alex Rodriguez	65	75	69.64
22-23	Alex Rodriguez	84	67	74.54
23-24	Hanley Ramirez	62	86	72.05
24-25	Eric Davis	64	130	85.77
24-25	Willie Mays	87	64	73.75
25-26	Willie Mays	71	78	74.34
26-27	Rickey Henderson	52	167	79.31
27-28	Barry Bonds	80	68	73.51
28-29	Barry Bonds	83	58	68.28
29-30	Alfonso Soriano	82	71	76.10
30-31	Barry Bonds	75	71	72.95
31-32	Barry Bonds	77	65	70.49

 

So Davis's 85.77 is 6.47 higher than the second best PS# of 79.3, belonging to Rickey Henderson. Davis accomplished this in 1986 (27 HRs & 80 SBs) and 1987 (37 HRs & 50 SBs). 

Over those two years, Davis had a .286 AVG, .389 OBP and a .560 SLG. He was only caught stealing 17 times, for an 88.4% success rate.

Here is the top 10 in OBP in the NL from 1986-87 for guys with 1,000+ PAs. Davis was 6th.

Tim Raines	0.421
Tony Gwynn	0.413
Keith Hernandez	0.395
Von Hayes	0.391
Mike Schmidt	0.389
Eric Davis	0.389
Ozzie Smith	0.385
Dale Murphy	0.382
Darryl Strawberry	0.379
Bill Doran	0.367

Now the top 10 in SLG. Davis is first.

Eric Davis	0.560
Mike Schmidt	0.547
Darryl Strawberry	0.547
Andre Dawson	0.528
Dale Murphy	0.526
Will Clark	0.521
Tim Raines	0.500
Kevin McReynolds	0.499
Tony Gwynn	0.488
Andy Van Slyke	0.484

Now OPS. Davis is first.

Eric Davis	0.949
Mike Schmidt	0.936
Darryl Strawberry	0.927
Tim Raines	0.921
Dale Murphy	0.908
Tony Gwynn	0.901
Will Clark	0.880
Von Hayes	0.868
Andre Dawson	0.860
Kevin McReynolds	0.837

Now OPS+. Davis was 2nd

Darryl Strawberry	151
Eric Davis	149
Mike Schmidt	148
Tim Raines	147
Tony Gwynn	147
Dale Murphy	139
Will Clark	139
Von Hayes	131
Keith Hernandez	130
Andre Dawson	127

Here is the top 10 in SB%, minimum of 40 attempts. Davis is 2nd.

Tim Raines	89.55
Eric Davis	88.44
Vince Coleman	85.71
Bob Dernier	82.69
Milt Thompson	82.28
Ozzie Smith	82.22
Tony Gwynn	81.58
Ryne Sandberg	80.88
Tracy Jones	80.85
Mariano Duncan	80.82

Davis only played 132 games in 1986 and 129 in 1987, for a total of 261. The next lowest total number of games for anyone else listed in the second table is 271 for Barry Bonds for ages 28-29. But Bonds only had a 68.28 PS#, far below what Davis had. 

Per 324 games, Davis would have a PS# of 106.48. Henderson would have 86.81. Soriano would have 79.28. These huge gaps show how great Davis was in 1986-87.

What if a player had 49 HRs over a two year period with a large number of SBs? It would not be enough to beat Davis. The most SBs ever over two seasons is 238 by Rickey Henderson. If a player had 49 HRs & 238 SBs, it would be a PS# of 81.27, still below Davis (in fact, Henderson hit only 19 HRs in the two years when he had 238 SBs which gives him a 35.19 PS#).

If a player had 49 HRs and 160 SBs, he gets a PS# of 75.02. Did any player ever do that? No. To get 160 SBs over two seasons, requires at least one of them with 80+ SBs. I looked at all such seasons and none of those guys reached 49 HRs over two seasons that included the 80+ SBs.

The most HRs over two seasons is 135 (by Mark McGwire). What if a player had 49 SBs and 135 HRs? His PS# would be 71.9. So again, not very close to Davis and I think any player who hit 100+ HRs over 2 seasons did not steal very many bases.

Henderson's best two year PS# with under 50 HRs was 66.96 over 1990-91 with 46 HRs & 123 SBs.