To second Alan's comments, unless you are using the odd and rare library that only works >2.5, or have enough and elaborate enough code using post 2.5 features (which is more of a risk for infrastructure oriented code than your average plug-in other than a few convenient decorators and shortcuts), I'd be surprised if your stuff didn't work in 2.5.
The migration from win to linux is more likely to give you some teething pains if you have path and asset management that isn't platform agnostic than the backporting from 2.65 to 2.5, and harder to test (just recede one of your win workstations to 2.5 and see if everything works for the latter). I'd be genuinely surprised if the next version, or its first SAP at the latest, didn't offer py2.7, it's more py3k that is going to be a much more intense, lancing pain in the arse, which most likely will require double clients (ala 32 and 64 bit times) for a while, but unlike 2.7, I don't think anybody is in danger of AD jumping on that bandwagon anytime this year. We'll be lucky if anything happens the next.
