Save yer money and stick with 4meg : 4meg and 10meg have the same upstream so in my opinion 4meg is better as you are capped @4meg you are less likely to saturate your upstream.
Ask yourself these questions :
* Where are you going to be spending this extra download bandwidth ? It can't be p2p as you already have the same amount of upstream and so will not gain too much... Ahhhh could it be a news server or other high availabilty source ?
* If so - it currently takes you ~3 hours to download a DVD but you want it an hour and 15 minutes - sounds cool : but after 24 hours you have downloaded near 18 DVD's and burnt 60Gigs of disk space - ask yourself do you really want to be spending your time sorting data and money on disk storage.
Personally I had 2 dedicated download machines - both high spec (they had to be) so that they could unrar / compress files without effecting download speeds.
Now that I've happily downgraded to 2meg I can do without that kind of grief and thinking how big a disk to buy.

Peace