Tests and discussions have gone on about this before. As I recall the general rule is this:
When multiple commands are being called:
statement condition {
commands
}
is faster than
statement (condition) {
commands
}
When a single command is being called:
statement (condition) command
is faster than
statement condition { command }
is faster than
statement (condition) { command }
is faster than
statement condition command
Whether that's still true, whether that's always true, and whether the speed benefits actually matter or not, I don't know.