I counter that with your post makes no sense?
Body roll has nothing to do with straight line speed? Where did you get that from? Grip in this respect also has nothing to do with straight line speed, we're talking about actual traction through corners here, neither track is wet for example.
The cars of lesser than F1 spec take less than a straight line through the corners as that's what physics dictates, they don't have the grip, they do have body roll hence them not being able to keep on the tight line?
And yes, they go through straight as they are riding the kerbs, they don't mind doing this, none of them exhibit anything like Jeremy Clarkson style of wagging tale and smoking tyres, your imagination has got the better of you.
Perhaps I've got the wrong end of the stick, perhaps you're trolling, perhaps a choice of words in my post confused you?