One problem I see is we’re using two different measuring units here. Your isp’s speed is measured in “b” bits, but BitComet uses “B” Bytes, which are a very different unit.
Now, your upload speed that you report as 0.7mbit/s, is this a confirmed “tested” speed, or advertised speed? You should use a confirmed tested speed for these calculations because adjusting to a faster “advertised” speed can result in all your available upload bandwidth being consumed, in which case all the best peers will assume you’re too slow to be bothered with and you’ll be passed up. In order to attract the best peers, you need to upload as much as possible, but also reply to requests immediately.
So, we need to convert from bits to Bytes, then reduce to about 80%, in order to get a good starting point. A shortcut you can use is to divide the bits by 10. In your case 700kb/s divided by 10 would be 70kB/s. This is a good starting point, but I’ll do all the math so you know how I reached this.
0.7mbit/s = 700kbit/s
700kbit/s divided by 8 = 87.5kBytes/s
If your speedtest is accurate, then this figure (87.5kB/s) is the fastest you can upload.
87.5 x 80% = 70
Set global max upload to 70kB/s
You should also keep in mind that your download speed will reflect this figure. On a torrent that isn’t saturated with highspeed users or a large number of seeders, your download speed will run at more or less this level. If a task has a good number of seeders or high speed users, then you will see speeds averaging twice this (70kB/s from peers who reciprocate and another 70kB/s from seeders). If a task has a large number of LTseed peers, then you could see the speeds over 2000kB/s that you reported prior, however for there to be LTseed peers available, that means that bitcomet peers have already downloaded this task and it’s moved into LTseed status. If this is a brand new release as you report, then it isn’t likely to have a lot of LTseeds.
So basically, some tasks will be super fast, some will be slow, and the best you can do is get your setting to the most efficient levels to match your connection. I’d recommend as a test you should try downloading OpenOffice torrent. Besides being a good torrent to test your speed (they are seeded by high speed servers), it’s also a great (and free) product.
http://distribution.openoffice.org/p2p/
One of their recent releases should download at your maximum download speed, assuming you’ve correctly setup bitcomet. You should also see improvements in other torrents, but some will be better then others, that’s just something you’ll have to live with being you have a very limited upload speed.