Best free UCI multi-core engine?

I have the following system:

4x AMD Phenom 2.30GHz with 4GB DDR2 RAM

I'm currently using Fire1.3.1 x64 KLO via Fritz XI interface from http://www.chesslogik.com/fire.htm and the hash table is set to 1024MB.

Can anyone suggest stronger multi-core engines for infinite analysis purposes?  I understand that Fire1.3.1 has Elo rating of around 3400.

I just dl'd Houdini 103.a

It is rated on some lists just below Rybka 4, in 2nd. It is also much faster than my Rybka 3 and 4--still testing this one.

Ok, looks good.

I'll give it a try & compare the 2.

What I did was compare analysis from a single game position after clearing the hash table, re-loading the engine & then infinite analysing it for 30 seconds, then recording the speed & depths reached:

1st run:

Houdini 1.03a x64 4CPU = 3725 KN/s Depth = 20/53

Fire 1.31 x64 4CPU = 3957 KN/s Depth = 18

Fritz 11 1Cpu = 1241 KN/s Depth = 16/32

2nd run:

Houdini 1.03a x64 4CPU = 3956 KN/s Depth = 35/41

Fire 1.31 x64 4CPU = 4132 KN/s Depth = 18

Fritz 11 1CPU = 1215 KN/s Depth = 16/32

It's an entirely arbritrary game & position, but here it is if anyone's interested to compare:

[Event "Biel Chess Festival"]
[Site "Biel SUI"]
[Date "2010.07.21"]
[EventDate "2010.07.19"]
[Round "3"]
[Result "0-1"]
[White "Parimarjan Negi"]
[Black "Fabiano Caruana"]
[ECO "A07"]
[WhiteElo "2615"]
[BlackElo "2697"]
[PlyCount "56"]

1. e4 c5 2. Nc3 Nc6 3. Nge2 Nf6 4. g3 g6 5. Bg2 Bg7 6. d3 d6
7. O-O Rb8 8. h3 b5 9. a3 O-O 10. Rb1 Bd7 11. Bg5 a5 12. a4
bxa4 13. Nxa4 Ne5 14. Nec3 Bc6 15. b3 Re8 16. Qd2 Qc7 17. Nd5
Nxd5 18. exd5 Bxa4 19. bxa4 Rb4 20. Ra1 Reb8 21. Rfe1 c4
22. Ra3 cxd3 23. cxd3 Rb2 24. Qe3 Rc2 25. Raa1 h6 26. Bxh6
Bxh6 27. Qxh6 Rbb2 28. Rab1 Qb6 0-1

I loaded the engines to analyse position at 22.Ra3 for the results above.

I think Firebird is the strongest engine available, rumored to have beat Rybka in several tests.

http://www.inwoba.de/bayeselo.html

IPON - BayesElo 0056 result:

List of best single engines, one engine per Author:

     Name                      Elo    +    -   games score oppo.  draws

   1 Houdini 1.03a *           2952   19   19  1000   73%  2790   34% 
   2 Deep Rybka 4              2944   13   13  2400   73%  2762   33% 
   3 Stockfish 1.8 JA          2895   13   13  2100   70%  2747   37% 
   4 Naum 4.2                  2815   10    9  3800   58%  2761   40% 
   5 Komodo 1.2 JA             2805   11   11  2800   54%  2774   40% 
   6 Deep Shredder 12 UCI 32b  2800    9    9  4600   57%  2750   38% 
   7 Critter 0.70              2785   12   12  2500   51%  2777   37% 
   8 Deep Fritz 12 32b         2783   10   10  3900   55%  2750   38% 
   9 HIARCS 13.1 MP 32b        2735   11   11  2800   44%  2776   37% 
  10 Zappa Mexico II           2710    8    7  7000   45%  2744   37% 
  11 spark-0.4                 2709   12   12  2400   41%  2779   36% 
  12 Protector 1.3.2 JA        2699    9    9  4600   42%  2759   37% 
  13 Onno-1-1-1                2683    9    9  4500   42%  2739   39% 
  14 Deep Sjeng WC2008         2672    8    8  5900   40%  2740   36% 
  15 Deep Junior 11.2          2668   12   12  2400   39%  2746   31% 
  16 Toga II 1.4 beta5c BB     2666    8    8  6300   41%  2733   38% 
  17 Loop 13.6/2007            2612    9    9  4400   35%  2719   37% 
  18 Twisted Logic 20100131x   2599   11   10  3600   32%  2729   30% 
  19 Spike 1.2 Turin 32b       2580    8    8  6100   32%  2712   33% 
  20 Crafty 23.1 JA            2546   11   11  3800   26%  2728   28% 

*The enigne is controversial. Please inform yourself to judge about it's legal status.

Maybe this link has the answer.

http://home.halden.net/mordor/tcec/index.php

Naum is in the lead at the moment, but it costs 60 Euro's.

Yes, but both Stockfish and Houdini are ahead of Rybka.

Stockfish 6