I started informational threads on both of these a few months ago. Since then I've been able to use each enough to get a feel for them (i.e. pushed the weight and capacity pretty far). Full details will end up in a to-be-written article discussing packs in depth. What follows is primarily meant to serve as a quick tool for folks considering buying one or the other.
Golite thread: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=59928&disable_pagination=1
Thruway thread: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=59678&disable_pagination=1
The Thruway has a lot going for it, but isn't quite a coherent package. My hope is the MH redesigns it a fair bit for next season, as with a few substantial tweaks it could be very competitive for several different user groups.
The materials are well chosen, and the pocket layout works well and is very versatile. The side pockets are easy to get at with the pack on, yet secure. The rear beavertail pocket would be much more useful if it were cut a few inches wider than the section of the pack it is meant to cover. As is they're the same, and getting something like snowshoes into the beavertail when the pack is full is not as easy as it quite frankly should be. The shoulder straps are excellent: the fit is ideal for me, and the foam is an ideal blend of supportive and cushy. The thin hipbelt gets the job done, but having the weight of a 1.5" buckle, lumbar pad, and velcro (to allow for hipbelt swaps) seems silly for a belt with such modest support. Beyond 20 or so pounds the belt lacks structure and starts to sag where it connects with the pack. I acquired MHs alpine hipbelt, which is probably the best hipbelt I've ever used on any pack, but unless steps are taken to substantially stiffen the backpad of the Thruway the alpine belt is overkill and cannot be put to full use.
The removable bivvy pad is a good idea which, like the hipbelt, fails to live up to what it could do. The dense foam of the pad in my pack is a great supplement to a sleep system, but rather heavy for what function it provides. I cannot testify concerning the reportedly rather different (lighter) pad which shipped with retail packs. The real problem is with the way the pad interfaces with the pack. The outward opening sleeve creates some uncontained/supported space which allows the pad to sag and buckle. The placement of the top compression strap tends to exacerbate this (see the photo of me skiing in the thread, above). In short, I would not want to carry much over 20 pounds in the Thruway as it is stock, and while the good points of the pack are substantial, the cost and weight do not in my book make those benefits worthwhile.
With the alpine belt and a burly framesheet (pictured in the Jam thread), the Thruway will carry well over 30 pounds with ease. Redesigning the pad sleeve to provide more structure, and having a combo of half bivy pad and framesheet along with a belt like the alpine (maybe a bit lighter) would make the Thruway a highly modular unit which could carry weight well and strip for lighter trips easily. I'd like to see the pack go in that directions.
The Jam is mostly a known quantity, with a design, fit, and feature set which checks a lot of boxes for a lot of people. With GoLites new aggressive pricing, nothing else even comes close. By fixing a few oversights, the new Jam could be far and away the best yet.
I discussed my difficulty with the hipbelt in the aforementioned thread. There are two issues here: that the current padding is too extensive for narrow waisted folks, and that the 1.5" buckle is in my opinion an anachronism for pack waist belts. It's not necessary for strength, bulky, and the pull-out nature of traditional buckles seems less secure and adjustable. The padding could be shortened by 3-5 cm on each side and fit a wide range of people better, and the buckle should be smaller, and possibly have at least one side which pulls from the belt rather than from the buckle. Generally the 2012 belt doesn't so much carry more weight than the 2011, is just carries it a lot more comfortably. It hugs the hips really well and generally gets the job done.
The other annoying nit which is really just oversight and nothing more is that the top strap is just barely long enough to close when the pack is full. It should be a good foot longer, to flexibly accommodate lashing a foam mat (or anything else) atop the pack. I cut the stock strap off and sewed a new one on, but that shouldn't be necessary.
The new framepad is thinner and denser than the 2011 model, but I don't think that's a good thing. The new one doesn't seem to facilitate carry better than the old one, and is less comfy as part of a sleep system.
The 2012 shoulder straps are also substantially less padded than the 2011, which seems like a poor choice. I've found the 2012 ones adequate, even carrying 30+ pounds, but folks with more sensitive shoulders will have a big problem here. The 2011 straps were for me perfect, and I'd encourage GoLite to bring them back.
On the whole the Jam is for me an easy pack to carry and work out of. I find myself grabbing it a lot because it is so user friendly for so many different things. If Golite can keep refining the formula they should keep selling plenty of packs.
Got questions? Ask 'em.