Tom I'm about 6'3" so I'm considering a poncho/rain pants combo (but what about the boots/feet?)
We're about the same height then. Rain pants should do the trick - or gaiters alternatively, if you decide to go that route. Wear rain pants over the boots to keep your feet dry.
Either way, good water repellent footwear is essential, preferably with a Goretex membrane. Pretty much any sturdy hiking boots should fit the bill. I'm somewhat partial to Meindl, but it's a fairly expensive brand. There are many good choices available on the market.
For summer hikes, I really like my ex-British army desert boots ("Soldier 2000" pattern). Bought a pair in as-new condition 8 years ago in London for a measly sum of 20 pounds, still going strong. Reasonably cool in hot weather, excellent fit (for my feet at least - this is a highly individual thing) and totally waterproof. I've even worn them in snow - in fact, I'm wearing them daily when commuting to work these days, no problems whatsoever.
For hardcore trekking though, I'd stick with a well fitting par of hiking boots, at least ankle height. And make sure to wear the right kind of socks. Something like wool or polypropylene, that will keep you reasonably warm even if your boots turn out to be less waterproof than expected.