Express Saver is 3 day shipping, by 7PM to residences -- always gets to me in two days. 2nd Day is guaranteed 2 days. Whichever one comes out cheaper when you count shipping would be the way to go.
The 1700+ is only a 1.47GHz frequency. The clock speed increase you may notice a small difference in framerate in games or anything else that has a specific timing system to show you how long it takes, but in most day to day things you wouldn't notice. However the 4X cache on the Athlon over the Duron should help even in things like web browsing and office apps, as those have always been helped by cache since they do repetitive instructions. If you do manage to overclock it to 2000+ speeds, that's still only 1.66GHz, but a 366MHz clock increase combined with the cache size should give you some noticeable gains overall. I personally probably wouldn't notice the difference in games, because I'm nearly blind anyway, but moving from a 1.2GHz MP to an XP2100+ made the system feel a bit quicker in general.
Keep in mind you'll want new memory unless you think yours will overclock as high as the CPU bus.