There is no guarunteed speed as has been stated, the only way you will get a guarunteed speed is through purchasing an expensive leased line like (ISDN - Expensive and Slow) (T1 - Expensive but quite fast) Good luck
80-90k/s download on a 750k connection is perfectly reasonable and you shouldnt really expect any more
10k/s upload with overheads and a few other people uploading on your UBR, again perfectly reasonable, and youre lucky, im lucky if my upload approaches 10k/s