Well, yeah, Im not surprised you have a bit of a struggle keeping up with a tandem Hobie. They have twice the paddling power that you do, in a boat only slightly heavier than a single kayak. Same principle applies in bicycling; there arent too many single cyclists who can keep up with a tandem crewed by cyclists of physical ability equal to the single rider. And the Feelfree Move ($545; feelfreekayak.com) is a stubby little thing.
REI Necky Manitou
While I have absolutely no quibble with a design such as Hobies pedal-powered Mirage Revolution ($1,600; hobiecat.com), Im doubtful that it would offer any speed advantage over what youre using now. Likewise, the Cobra Explorer ($460; cobrakayaks.com) is a perfectly fine sit-on-top. But I wonder if youd be better served by an enclosed kayak. It certainly would be fasteryoure lower in the water, less wind drag, etc. I can imagine that heat would be a factor in your area, but some boats have big, roomy cockpits that vent well.
With that in mind, Id certainly suggest you take a look at something such as the Necky Manitou ($799; necky.com). Its a hybrid" boat, one that you sit inside of like a traditional kayak, but that has more stability and a bigger cockpit. Its easy to paddle and you dont feel as if youre wearing the thing. Theres also a storage compartment for extra gear. I really think youd find it to be easier to paddle and keep up with your friends. Wilderness Systems Pungo 120 ($775; wildernesssystems.com) is similar, as is the Dagger Blackwater 12 ($679; dagger.com).