As for indicating thermals, think of a high-wire balancing act. A long pole with large effective "force" on the ends provides resistance to changes in "pitch". A short broomstick will "pitch" wildly and the guy will fall off the wire. A nose heavy plane with opposing elevator force will mush right through a thermal and you might not even see any waggle at all. If balanced, it'll take less force to "upset" it and it'll waggle much more pronounced.
As far as overall speed through a thermal being a factor, I'd say sure, given it is fast enough
although a couple mph may not matter. However, a nose heavy plane can't really reach best min. sink speed and won't be nearly as "floaty".