Seaboard (SEB) had the highest return between 2004 and 2005 by a mid-cap US stock, returning 440.3%.

ASSET	YEARS	% RETURN
Seaboard (SEB)	2004-2005	440.31%
HF Sinclair (DINO)	2004-2005	336.18%
BRF SA ADR (BRFS)	2004-2005	314.38%
United States Lime & Minerals (USLM)	2004-2005	278.14%
Frontline (FRO)	2004-2005	253.41%
Cleveland-Cliffs (CLF)	2004-2005	251.38%
U-Haul (UHAL)	2004-2005	246.48%
VSE (VSEC)	2004-2005	229.06%
Cavco Industries (CVCO)	2004-2005	227.6%
Forward Industries (FORD)	2004-2005	222.46%
Hub (HUBG)	2004-2005	222.39%
Boyd Gaming (BYD)	2004-2005	198.16%
Transocean (RIG)	2004-2005	190.37%
Penn National Gaming (PENN)	2004-2005	185.02%
American Eagle Outfitters (AEO)	2004-2005	182.3%
Denison Mines (DNN)	2004-2005	182.08%
NOV (NOV)	2004-2005	182.05%
Turkcell Iletisim Hizmetleri AS (TKC)	2004-2005	180.7%
Gildan Activewear (GIL)	2004-2005	177.52%
Gerdau SA ADR (GGB)	2004-2005	173.82%
Seabridge Gold (SA)	2004-2005	172.46%
Abercrombie & Fitch (ANF)	2004-2005	168.85%
Urban Outfitters (URBN)	2004-2005	168.11%
Liberty Global (LBTYA)	2004-2005	164.47%
Tutor Perini (TPC)	2004-2005	161.08%

Mid-cap stocks are treated as having a market cap between $2B and $10B.