Personally I really, really, really doubt it has to do with location. It affects for sure, but only if your connection is lagging in terms of seconds. Otherwise, even if you are connected from the most remote part of the planet you'll still have 300-400ms ping times which is not enough to raise stales to 5%. I have 0.2s ping times and I'm like at 0.5% reject rate. When I emulate further delay by increasing bandwidth load in my adsl line, I don't get significantly more. So latency is clearly a lesser issue.
Run a cpuminer for a test and check its stales. If it's the same percentage after a day, you are right. If not, there's something wrong with GPU settings.
Okay you have me doubting my previous conclusions so I did some testing. Below are the results with intensity different by 1 level. I only ran these for 2 to 3 hours on each setting so it's not really a big enough sample size to draw firm conclusions about the rejects, but there seems to be a slight overall improvement on the lower intensity setting, accompanied by a whopping 23% drop in total hash rate, 50% in the case of GPU 2! I can go as high as I:16 on GPU 0 and GPU 1 before all hell breaks loose. I've never run a CPU miner, will give it a go when I find some more time.
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[P]ool management [G]PU management S]ettings [D]isplay options [Q]uit
GPU 0: 62.0C 1786RPM | 1.535M/1.535Mh/s | R: 1.9% HW:0 WU:0.020/m I:12
GPU 1: 60.0C 1256RPM | 1.535M/1.534Mh/s | R: 3.6% HW:0 WU:0.022/m I:12
GPU 2: 81.0C 2935RPM | 477.8K/483.3Kh/s | R: 1.4% HW:0 WU:0.008/m I:10
GPU 3: 48.0C 40% | 1.100M/1.099Mh/s | R: 3.8% HW:0 WU:0.015/m I:13
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[P]ool management [G]PU management S]ettings [D]isplay options [Q]uit
GPU 0: 65.0C 1893RPM | 1.879M/1.880Mh/s | R: 4.1% HW:0 WU:0.025/m I:13
GPU 1: 62.0C 1314RPM | 1.882M/1.880Mh/s | R: 2.0% HW:0 WU:0.028/m I:13
GPU 2: 78.0C 2610RPM | 942.6K/944.7Kh/s | R: 4.0% HW:0 WU:0.013/m I:11
GPU 3: 44.0C 40% | 1.403M/1.402Mh/s | R: 4.6% HW:0 WU:0.020/m I:14
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