Sarah,

the 17 has a simple hull shape and from a holder perspective does just fine with foam blocks over whatever bar you can get up there.  (see the $50.00 kayak foam pad option on the CLC website - search for kayak rack).  i regularly car-top with this system (two to three times a week including highways).  this is a simple, bullet proof approach and no worries about complex, expensive parts.  just as, if not more important than the rack, is making sure your tie downs are tight and secured and properly securing a bow and stern line which often is the more difficult issue on newer cars (finding an anchor point on the vehicle).

of course there are more expensive/complex systems and these work well to.  I use the thule system with gliders on one of my cars becuase it is easy for my daughter to slide her boat on this single handed. 

Thanks for the info Hs, I am using a foam bolck system with the strap coming through the car now and its enough for me to travel the 30 miles to my favorite spot.

My concern is taking my boat to longer distance at highway speed or even adding my 15' aliminum canoe along, so a J style of mount is what I am considering.

Sarah,

Any of the systems should be secure at highway speed/distance.   As i mentioned, i routinely use the foam block system on the highway which includes up and down HWY 95 going between DC and NY (as do many of my paddling colleagues).  and by a foam block system, i mean a foam block over a bar/attachment system (which in my case is aThule).

the more complex systems (than a foam pad over a bar) typically add some additional feature such as being able to get more boats on the roof than you can in a simple flat system (e.g., by putting the boat up on its side) or helping making it easier to get the boat on the roof by either folding down or having rollers or gliders.  these 'above the bar' attachments often cost as much as the bar/car attachment itself.

the most important/essential element of any system is the bars and the attachment points for that (and how it integrates with the car).  after the bar, the disadvantage of the more complex systems is they typically put the boat higher in the air (and thus more stress on the bar/vehicle) and have multiple parts that can fail and create an accident (outside of the bar/car attachment itself).  most reputable companies like Thule/Yakima will have a system that will safely allow you to set up a bar on the car at a reasonable price. 

so what i was referring to above is what you do after you have selected a bar/attachment system.  a simple foam block is one of the simplest, flexible and secure systems.

most cars/bars can easily accomodate two kayaks (or a kayak/canoe) laying flat...so a j system may not be adding any real capacity relative to its complexity. also, since a j system puts the boat higher in the air and the boat is not symmetrical to the airstream, it puts more stress on the whole system which is generally something you are trying to avoid. 

I carry a 16 and a 17 side by side on my subaru forester and occasionally on an impreza using the foam blocks and tying to the roof rack , one strap just in front of the cockpit and one just behind, and then bow lines only.  Have gone 400 miles at 70 MPH without problem.  If you make sure you put a twist into the straps as they leave the sheer for the bars  you can stop the Buzz that will occur if the strap is not twisted.  have also carried on kayak on an escort without roof rack using the strap through the doors and bow and stern lines.  worked fine at 70 MPH.  On one firends car with no place to hook under the bumper, I ran a strap under the hood behind the latch, then slammed the hood and used that for bow tie down. It also worked.  Kayaks are made to cut through water. Wind is thinnner.

Just stop after about 15 minutes and check the lines and tighten if they loosen.  After the first adjustment you should be good for the rest of the run.

PS: I once used a rope to lash 2x4st to the cross bars to extend them, carried a canoe upside down in the middle and a kayak on its side on each side of the canoe, Then multiple straps. i think the canoe had its own and the kayaks were under two long straps  going over the whole assembly.  Even that worked at 65.