Hi
the tires on the speed d7 are not THAT bad .... you will see marginal improvements when you get a new schwalbe tires, but its not like adding 100 hp ..lol The Schwalbe Big Apple fits your bike although the fender cleaance need to be "wiggled" with ... but they will fit The big apples have a nice suspension built in , which your current tires are not so much ....

But I am kinda frugal ( although I selling these things ..lol ) and I would suggest that you put serious miles on your currentones in order to maek the switch

Slick tires versus knobbies ..most of it is in your head .. the contact patch of the tire is about a penny ..it doesnt make a lot of difference what kind of profil you have ( exception mud and snow where knoobies will give you more grip as the knobs sink in and the contact patch is biggger ... but for the road slicks are the way to go ...

when you see cord its time to buy some new tires ... you will see when its time ...

thor