The custom list method property will not speed up listing.
However here is a complete list of params that can be used provided the ftp server supports them. (FlashFXP might not be able to handle the output returned from some of these methods)
Code:
-a, --all do not hide entries starting with .
-A, --almost-all do not list implied . and ..
-b, --escape print octal escapes for nongraphic characters
-B, --ignore-backups do not list implied entries ending with ~
-c sort by change time; with -l: show ctime
-C list entries by columns
--color[=WHEN] control whether color is used to distinguish file
types. WHEN may be `never', `always', or `auto'
-d, --directory list directory entries instead of contents
-D, --dired generate output designed for Emacs' dired mode
-f do not sort, enable -aU, disable -lst
-F, --classify append a character for typing each entry
--format=WORD across -x, commas -m, horizontal -x, long -l,
single-column -1, verbose -l, vertical -C
--full-time list both full date and full time
-g (ignored)
-G, --no-group inhibit display of group information
-i, --inode print index number of each file
-I, --ignore=PATTERN do not list implied entries matching shell PATTERN
-k, --kilobytes use 1024 blocks, not 512 despite POSIXLY_CORRECT
-l use a long listing format
-L, --dereference list entries pointed to by symbolic links
-m fill width with a comma separated list of entries
-n, --numeric-uid-gid list numeric UIDs and GIDs instead of names
-N, --literal print raw entry names (don't treat e.g. control
characters specially)
-o use long listing format without group info
-p append a character for typing each entry
-q, --hide-control-chars print ? instead of non graphic characters
-Q, --quote-name enclose entry names in double quotes
-r, --reverse reverse order while sorting
-R, --recursive list subdirectories recursively
-s, --size print size of each file, in blocks
-S sort by file size
--sort=WORD ctime -c, extension -X, none -U, size -S,
--time=WORD show time as WORD instead of modification time:
atime, access, use, ctime or status
-t sort by modification time; with -l: show mtime
-T, --tabsize=COLS assume tab stops at each COLS instead of 8
-u sort by last access time; with -l: show atime
-U do not sort; list entries in directory order
-w, --width=COLS assume screen width instead of current value
-x list entries by lines instead of by columns
-X sort alphabetically by entry extension
-1 list one file per line