Tire upgrade

I've got four years and a few thousand miles on the original Primo
Comets on the Limbo. The front is 20 x 1.75(406mm) and the rear is a
26 x 1.50(559mm). I'm planning on doing a century ride in mid
September, pogo-ing al the waaay!(think Christmas song here).
Anyway, I'd like to have some fresh tires and tubes, hopefully with
less weight and/or rolling resistance. How narrow could the tire on the
front get before worrying about already sketchy traction issues become
serious? On the other hand, does a tire like the Tioga Comp Pool with
it's apparently insanely low rolling resistance make up for the weight
and traction of the tire? The Stelvio or Grand Prix tires look like
the obvious choice for the desired results, but again, how are these
tires for traction on the front?

Best regards,

John

Ordered the Stelvios, plus new tubes.

John