Unusual byte sequence for setting R8 - 128

In a piece of system code (in Delphi) I found this sequence ($ stands for "hex"):

    DB      $49,$C7,$C0,$80,$00,$00,$00  // MOV  R8, 128

      

        
        
        
      

    

Indeed, it sets from R8 to 128 in the debugger. But it won't:

    MOV     R8D,$80 // or $00000080

      

        
        
        
      

    

do the same thing? Is there something special about the previous byte sequence (speed, setting some flags, etc.) that would make the author of the code prefer it over R8D?

A bit more code upon request:

// RAX/XMM : 16BYTES VALUE. RDX: COUNT. RCX: DEST. ADDRESS. (16BTYES ALIGNED)
@@COPY128:
        DB    $49,$C7,$C0,$80,$00,$00,$00  // MOV  R8, 128
        CMP   RDX,R8
        JL    @@COPY64
        SUB   RDX,R8
        DB    $0F,$1F,$80,$00,$00,$00,$00 // NOP DWORD PTR [EAX + 00000000H] ; NOP(7)
@@COPY128LOOP:
        MOVDQA [RCX      ],XMM0
        MOVDQA [RCX + $10],XMM0
        MOVDQA [RCX + $20],XMM0
        MOVDQA [RCX + $30],XMM0
        MOVDQA [RCX + $40],XMM0
        MOVDQA [RCX + $50],XMM0
        MOVDQA [RCX + $60],XMM0
        MOVDQA [RCX + $70],XMM0
        ADD   RCX,R8
        SUB   RDX,R8
        JG    @@COPY128LOOP
        ADD   RDX,R8

@@COPY64:

      

        
        
        
      

    

This is part of a procedure called _FillChar

that fills a piece of memory in multiples of one byte (or char), more or less similar to memset()

in other languages.