If the software can't do an AP29, is an AP28 possible? If so, I vote we keep going. There are more AP27s out there still. Just sayin'.
I am wondering about the nature of the limitation on 29. Would looking for AP29's require bigger work units and so may be it would be appropriate to move the project to GPU only if the required software changes were made?
AP29 requires difference divisible by 29 which makes the search 29 times harder.