It could be faster:

    lda #firstbyte
    sta dest+0
    lda #secondbyte
    sta dest+1
    etc.

6 cycles per byte, so 166KB/sec. But we can do better: there are only 256 different bytes, so group the stores by byte value so that you don't have to reload before each one:

    lda #0
    sta dest+10  ; All the places that get 0
    sta dest+29
    sta dest+42
    lda #1
    sta dest+3   ; All the places that get 1
    sta dest+82
    etc.

Up to 250 KB/sec and less space. If the prior data in dest is known, it could be even faster: skip stores where the destination already has the correct data. And even faster: for video, skip stores which have a low hamming distance from the prior bytes and put up with a bit of noise..