Don't think 40W is underpowered. It's really, really not.
Hard to believe, but very very true. I have a 5210, and it has a bar graph, so you can have an idea of power flow.
When powering up a cartridge from cold, the graph usually saturates around 60-70% for a 700-series cartridge (even the large ones like the hoof or the 5mm chisel). Even the massive desoldering heads don't pull more than 70-80%. So assuming this is linear, with 40W, you'll get cold-to-700F in 6sec instead of 5s?
Then, once hot, forget it. Putting the full-size hoof tip on a solid piece of metal with lots of solder to make contact, you'll peak at 40-50%. And a square cm2 solder blob on that solid piece of metal will go cold>liquid in a couple of seconds.
So... 40W should do just fine. It'll still be ridiculously fast.
One thing to note is that the price of the old 5000 or the new 500 are not that much lower than the 5200.
Also note that the new Metcal supplies use switching power supplies, so you can use US-bought units anywhere. Might be worth importing if the import duties make sense (also, Metcal sells refurbished units in the US at a good price - contact them for that).