As Parky suggests in "awkward mode", if you want to stay dry during prolonged downpours then the only way to do it for sure is stay inside.
Look what paddlers use to ensure their bodies stay completely dry, and it's a formal dry suit with tight rubber seals aroudn the neck and wrists. Spend much time walking up a hill in the like and you'd be bathing in your own sweat quite soon. The moral is don't assume you can stay completely dry, because there are often conditions where it just isn't possible. Water will get in through the big holes your head, hands and trunk come out of and water you've sweated out often won't be able to get out, whatever marketing may say about miracle super-duper-tex it's made of.
What you can reasonably expect is something that will keep you dry enough in the worst conditions that you don't get chilled or especially uncomfortable, and you'll get that from a huge number of different garments. Try things on for size, as fit and cut will determine a great deal of the comfort and you can't just assume that something from Brand X will fit: their tailors' dummies aren't neceassrily the same shape as you.
the lightest fabrics, like Goretex Paclite, tend to lose a great deal of breathability when thier very light face fabrics are saturated, so something a little heavier will probably be more comfortable in prolonged and/or heavy rain. More elaborate hoods add to the cost but keep out wind blown rain better. If you want to stay as dry as possible you'll need to combine a jacket with trousers, and quite possibly gaiters too: a jacket isn't enough on its own.
Don't rule out umbrellas: not much use in high winds, but if it's heavy rain and no wind they're better at keeping you dry than any jacket on the market at any price.
Pete.
