remember places that say 'no commission' will have worse rates; that's how they make their money. The other way round, places that do charge commission may have better rates but how good they are may depend on how much you want to change. Faffing around with a calculator and 16 different exchange rates can be more trouble than it's worth sometimes.
My guess is the dollar rate won't get much better (from your point of view) in the next 9 months and is more likely to get a bit worse, but remember the money will be in dollars in your purse rather than pounds earning interest in your bank, so it may not make much difference.