How long will the speed stay up to the limit?

http://www.bandwidthplace.com/
http://www.speedtest.net/
Speedtouch-DSL ===>	Dlink Router ===>	XP desktop
Date Time	IP Address	Download	Upload	Ping	Server	comments
2012-03-11 08:44 EDT	172.129.54.12	4.79 Mb/s	0.41 Mb/s	127 ms	Wichita, KS	Fire Fox * * * *
2012-03-10 19:35 EST	172.129.54.12	5.08 Mb/s	0.37 Mb/s	180 ms	Wichita, KS	Fire Fox * * * *
2012-03-10 16:05 EST	172.129.54.12	4.91 Mb/s	0.41 Mb/s	128 ms	Wichita, KS	Fire Fox * * * *
2012-03-10 09:55 EST	172.129.54.12	4.45 Mb/s	0.41 Mb/s	129 ms	Wichita, KS	Fire Fox
2012-03-10 09:18 EST	172.129.54.12	4.19 Mb/s	0.40 Mb/s	138 ms	Wichita, KS	Fire Fox
2012-03-10 09:18 EST	172.129.54.12	4.19 Mb/s	0.40 Mb/s	138 ms	Wichita, KS	Aol 9.6 3x try's