Код:

@ECHO OFF
Set input=4
Set output=2
Set ext=txt

FOR %%i IN (%ext%) do CALL :MVFILE "%%i"
GOTO :EOF

:MVFILE
If "%~z1"=="" GOTO :EOF
IF %~z1 GEQ 300000 (
	For /F "UseBackQ Delims=" %%I In (`Dir "%input%" /B 2^>Nul`) Do For %%K In (%ext%) Do If /I "%%~xI"==".%%K" Call :_copyF "%%I"
Exit
ECHO %1, size=%~z1 
:_copyF
Set cn=
:_loop
If Exist "%output%\%~n1_%cn%%~x1" Set /a cn+=1& Goto _loop
Move "%input%\%~1" "%output%\%~n1_%cn%%~x1">Nul
GoTo :EOF


::) ELSE (
::	move %1 "c:\test\3\"
::	ECHO %1, size=%~z1 
::)
::GOTO :EOF