Why move? If you really need a feature of 5.8.x then fine. If not remember the old axiom: If it aint broken, don't fix it. As noted 5.8.x can benchmark a lot slower than 5.6.2 - as I understand it this is largely to do with all the unicode related internal changes.

Ideally you should have a full test suite so you can just put up 5.8.x, run the suite and relax. If not developing such a suite would be a good idea before you contemplate moving.

The major change to be aware of is binary incompatibility between 5.6.x and 5.8.x What this means is that every non (ActiveState) core C based module you have installed will need to be reinstalled before it has any chance of working. DBI, DBD::xxxx Digest::xxxx any many others fall into this category. Also you may need to have cl.exe handy as ActiveState no longer supplies PPMs for encryption modules so you may need to compile them yourself (unless you can find a PPM elsewhere)