Nooooo: don't touch the cyclon 5000. Got four of the buggers, had them for about a decade, and the only good thing about them is that they're easy to service. Quite handy as when I was diving a lot of grotty sumps I'd have to strip them down three times a year. Two disadvantages with the cyclon 300: they're like rocking horse poo and they can be a bit tricky to service (tend to damage the seat when you try to remove it).
(300 refers to the old, unbalanced first stage-the bit that attaches to the bottle; the 5000 is a more modern, balanced first stage). Real shame about the 5000 is that they're very nice bits of kit but they're too sensitive to survive proper caving. In my opinion, obviously. And most other people who've ever felt the need to twat their regs with a bolting hammer when they're on the wrong side of a sump!
One idea that the manufacturers don't like (but I swear by) is mix and match. I use cyclon 2nd stages (bits that go in your gob) attached to the most basic 1st stage money can buy (in my case a Scubapro something or other). You need to tweak the regs a bit but there are plenty of helpful types out there who could help. Seriously, though, if you're just thinking about short, simple sumps then just go for anything that's cheap, simple, and reliable. To get your shiny 5000 serviced in a dive shop you're looking at a ridiculous price of about £60 plus. Really not worth it. Hope this helps. If nothing else it'll make you realise that every diver out there has a different opinion...
By the way, is "Mike W" the Mike W that I'm thinking of? Hope you're coming to the BCRA do?
Joel