|"My DSL when wired direct shows 100Mbps"|
Of course it does & if you had a Gigabit ethernet card, it would show 1000Mbps. All that shows is what it's capable of, it doesn't mean it's actually transferring data at that rate. What rate does your DSL provider supply?
"signal from my Linksys Wireless B (BEFW1154) drops to 11Mbps"
You have a wireless B. The max transfer rate is 11Mbps. There is nothing wrong, that's all it's capable of.