How far apart should I do 2 IM’s in one year?

I’m planning on doing 2 ironman length races next year, I have registered for IMAZ in early April and need to decide on a fall race. There are three alternatives that are either a 1 day drive or a cheap direct flight away:

  • IMC end August (21 week gap between races)

  • Grand Columbian mid September (24 week gap)

  • Silverman mid November (32 week gap)

Any suggestions on how far apart the races should be? I need to decide by Aug 29th or IMC 2006 will no longer be an option.

There is Duke in October as well. Assuming it will be around next year.

The Duke doesn’t meet my criteria of being able to drive there in 1 day or take a cheap non stop flight.