The Sync Speed shown by the router is the actual bandwidth you are provided with down the line. Speedtests can only measure your throughput of actual data as it occurs; this excludes all the overheads that Internet Protocol needs to add to the data for routing and packaging purposes. Usually throughput is about 83-4% of Sync Speed; so you should be getting about 6200 Kbps.
Significantly lower speeds could be caused by your ISP throttling you or congestion at the exchange or elsewhere. Have you tried various speedtests?
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU BB => 2010: Orange 19 Meg Tweaked / 16 Meg Untweaked LLU BB