and they are just overclocking animals! set them to 5,5,5,15 and you will be able to go up to 500fsb (ddr2 1000) at 2.2volts!
make sure you run memtest86+ 1st to be sure you mem are legit with no errors. the ones you picked are good, but just throwing something else out there and as you can see they are at a good price. better than what i paid for!
doubletake has posted the better deal, but the memory in your second link is better due to being guaranteed to run the tighter timings (though at higher voltage, IF you raised the voltage on the first linked memory it too might run at tighter timings and/or higher bus speed.
Personally I'd rather have 4GB of mediocre memory than 2GB of fast memory, having another 2GB to cache disk IO so much better makes a system a lot smoother running and enjoyable.
Why sit around worrying whether you're going to get burned on a rebate? Well the thing is, you won't get burned on most rebates and there is no need to worry about it because when all is said and done, you still come out financially ahead buying products with rebates even if a small percentage of them don't get paid. Just don't try put yourself in a bind needing any given rebate to come in, in order to pay bills any given week or month.