Hi John,
well I have used both in 4", I currently have the clear hose on my PT (because i purchased a longer length and therefore gives me a better reach to my chip extractor.) Its been in use for a couple of years in an unheated workshop and has shown no sign of failure, I don't stand on it though!
The clear hose seems a little more flexible than the grey stuff & you can see the chips passing through the clear stuff but it will get a little dusty on the inside.
I have just brought some 21/2" Dakota hose from Rutlands when they had it in a sale, I thought that was heaver duty which was what I was originally after when I got the clear stuff from Axminster, the Dakota hose has a nylon 'spring' which I guess would take a bit more 'crushing' before it distorts & flattens. I would say its is probably less flexible than the Axminster hose though.
At the end of the day I am sure you will find any of the hose will do - you might find 2.5 meters a bit short if you are running it along the floor.
Hope this helps,
Mike