Lighter alternative to Schwalbe Marathon Plus?

I've got 700x38c Marathon Plus's on a bike I've been putting together. Combined with the NO-BS rims, the weight and inertia seems mismatched with the rather lively Koga Miyata frame, and the rolling resistance is impressive.

I'm planning a short 300 mile first "tour" this summer on reasonable pavement. Weight on the tires with me, the bike and stuff might approach 340lbs.

My initial thought was to pick up 3 folding Panaracer PT Paselas.

Any suggestions would be appreciated.