Frontline (FRO) had the highest return between 2004 and 2007 by a mid-cap US stock, returning 3,535.5%.

ASSET	YEARS	% RETURN
Frontline (FRO)	2004-2007	3,535.49%
BRF SA ADR (BRFS)	2004-2007	2,107.18%
Companhia Energetica de Minas Gerais CEMIG Pref ADR (CIG)	2004-2007	1,440.74%
BlackBerry (BB)	2004-2007	913.1%
Companhia Siderurgica Nacional ADR (SID)	2004-2007	870.45%
Mosaic (MOS)	2004-2007	824.91%
RadNet (RDNT)	2004-2007	822.73%
Range Resources (RRC)	2004-2007	722.71%
Cleveland-Cliffs (CLF)	2004-2007	715.12%
Gerdau SA ADR (GGB)	2004-2007	689.72%
Icahn Enterprises (IEP)	2004-2007	678.28%
VSE (VSEC)	2004-2007	672.79%
HF Sinclair (DINO)	2004-2007	665.24%
Riot Blockchain (RIOT)	2004-2007	658.26%
Transocean (RIG)	2004-2007	637.07%
Allegheny Technologies (ATI)	2004-2007	579.6%
NOV (NOV)	2004-2007	560.91%
Turkcell Iletisim Hizmetleri AS (TKC)	2004-2007	542.81%
ICL Israel Chemicals (ICL)	2004-2007	536.65%
CNX Resources (CNX)	2004-2007	473.64%
Gildan Activewear (GIL)	2004-2007	433.16%
Seaboard (SEB)	2004-2007	427.51%
Itron (ITRI)	2004-2007	422.71%
Carpenter Technology (CRS)	2004-2007	420.5%
Penn National Gaming (PENN)	2004-2007	415.14%

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