simple words u cant replace 1000cc with a 660cc, I always advise to go for 1.0 L if u have the budget, unless the gadget of 660cc Custom Variants are mesmerizing you, then its up to you.
660cc are good to go on most practical routes as for hills, never used them but lets ask @Wanderlust he owns a Nissan Kixx and travels North a lot.
wassalaam