Using the script found in this post, I retested.

Turns out, you lose.

Results in mIRC v6.14:
Code:
-------------------
* IF speed test: 10,000 iterations per test
-() -{} single 641
+() -{} single 731
-() +{} single 781
+() +{} single 791
-() +{} multi 801
+() +{} multi 811
-------------------
* IF speed test: 100,000 iterations per test
-() -{} single 6389
+() -{} single 7420
-() +{} single 7911
+() +{} single 7991
-() +{} multi 8141
+() +{} multi 8192
-------------------

Omitting both ( ) and { } is demonstrably faster, but it is also much harder to avoid ambiguity. Thus, these results show that the forms to use, in fastest-to-slowest order, are as follows:
Code:
  if a == b command
 
  if (a == b) command
 
  if a == b { command }
 
  if (a == b) { command }
 
  if a == b {
    command
  }
 
  if (a == b) {
    command
  }

Get your facts straight before setting yourself up as some sort of expert. The fall from the heights hurts more from that distance than down here where us coders live. Also, bear in mind that these statistics need to be retested with each new version because they do change sometimes; it's always best to check yourself before making such a fool of yourself, though we all do it occasionally.