この場合だったらmemcpyが速そうな感じ
#include "winmm.as"
#define timeStart timeGetTime : st = stat
#define timeEnd timeGetTime : et = stat
#define ctype time ((1.0 * et - st) / 1000)
// -----
sdim date, 1100000
notesel date
timeStart
repeat 10000
noteadd "テスト",cnt,1
loop
timeEnd
mes "noteadd : \t"+strf("%.3f",time())+"s"
// -----
sdim date, 1100000
timeStart
repeat 10000
date+="テスト3\n"
loop
timeEnd
mes "文字列連結 : \t"+strf("%.3f",time())+"s"
// -----
sdim date, 1100000
src = "テスト3\n"
offset = 0
size = strlen(src)
timeStart
repeat 10000
memcpy date, src, size, offset, 0
offset+=size
loop
timeEnd
mes "memcpy : \t"+strf("%.3f",time())+"s"