generally speaking, when your upload speeds aren't limited, your download speeds will be faster. I don't recall the technical reason for this but I did read it on a network-technical site somewhere (not BT-related). So naturally, for BT, you're going to see slower speeds during a download if your upload is capped.
If you're on a registered-member BT site, you may see ratios and kept stats. This doesn't affect your speeds but it does affect your standing with some of those sites. Some people with lower ratios may experience wait times or even bans if it is too low. But that's about it. If you are a very giving person with even a 1:3 ratio (usually stated as 3.0), it won't give you any kind of advantage over someone who has a 1:1 (1.0) ratio. Well, maybe not completely true... at least you can leech that much more without having to upload anything and you're still in the green.
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