EBay (EBAY) had the highest return in October 1998 by a large-cap US stock, returning 95%.

ASSET	MONTH	% RETURN
eBay (EBAY)	October 1998	95%
Telkom Indonesia (Persero) Tbk PT ADR Rep 100 B (TLK)	October 1998	84.1%
Teradyne (TER)	October 1998	79.93%
ASML Holding NV ADR (ASML)	October 1998	74.36%
PTC (PTC)	October 1998	66.25%
Mitsubishi UFJ Financial Group Inc ADR (MUFG)	October 1998	59.19%
Morgan Stanley (MS)	October 1998	58.03%
HEICO (HEI.A)	October 1998	52.17%
KLA-Tencor (KLAC)	October 1998	51.28%
Flex (FLEX)	October 1998	50.54%
Skyworks Solutions (SWKS)	October 1998	49.44%
MasTec (MTZ)	October 1998	49.41%
Heico (HEI)	October 1998	48.87%
Fastenal (FAST)	October 1998	48.21%
Incyte (INCY)	October 1998	46.99%
Cognizant Technology Solutions Corp Class A (CTSH)	October 1998	46.28%
Barclays PLC ADR (BCS)	October 1998	46.25%
Lam Research (LRCX)	October 1998	46.17%
Korea Electric Power Corp ADR (KEP)	October 1998	45.71%
Coca-Cola Europacific Partners (CCEP)	October 1998	44.72%
Applied Materials (AMAT)	October 1998	42.31%
Rogers Communications (RCI)	October 1998	42.04%
STMicroelectronics NV ADR (STM)	October 1998	41.42%
Sarepta Therapeutics (SRPT)	October 1998	40.82%
Coca-Cola Femsa SAB de CV ADR (KOF)	October 1998	40.43%

Large-cap stocks are treated as having a market cap of $10B+.