i have DSL, and my mom has cable. they both have their advantages and disadvantages really. cable can be slow if a lot of people on cable in your area are downloading, uploading, etc., whereas a dsl line is dedicated for you, what others are downloading won't affect your connection.
caps vary by isp. my dsl is capped at 1500/256, which is 150k download and 25k upload.
given the choice between the two, usually i would pick dsl, because it's a dedicated line. but, if you can get faster speeds from cable for the same price or less, then go for that.
for their ultra high speed, you would probably get around 290 - 300k down, and 60-65k up, which for the price, that's not bad at all. what they mean by cap is just how high you can go. you're capped at 3000/650, meaning you can't expect speeds of 4000/1000. your max upload speed under ideal conditions, good line quality, good routing, etc. would be 65k, what you're capped at.
another place you can look is here:
http://www.dslreports.com/forum/sympat
and see what other users say about that isp