** BMO downgrades CSX CSX.O to "market perform" from "outperform", maintains PT at $38

** "We believe there is significant uncertainty surrounding key details of any potential deal involving CSX" - brokerage

** Sees BNSF merger deal as CSX's "best M&A scenario", adding that such a deal would have a greater chance of regulatory approval

** 18 of 28 brokerages rate the stock "buy" or higher, 10 "hold"; their median PT is $39 - data compiled by LSEG

** Including session's move, CSX up 12% YTD

(Reporting by Apratim Sarkar)

((Apratim.Sarkar@thomsonreuters.com))