Steve, I've already said in the past that I was into volunteering some 168 TSX bullets for you, and even helping out, if you needed any assistance.
As for the .300 Magnum discussion, this is something I have also been pondering for some time, but now more than ever because I'm putting a new barrel in .300 Winchester Magnum on a hunting P-14. Because of the age of this rifle (literally approaching 100 years), I've made it a policy never to load it to the redline, but instead load to the level of a very hot .30-06. With its original barrel, for example, I loaded it with 150-grain Hornadys at about 3,100, but I only ever used it for paper punching (where it shot better than most fancy new rifles with premium factory ammunition).
I can say this: for my main .300 Winchester Magnum -- a Sako L61R Finnbear with a 22.5-inch barrel -- the load I've settled on for all purposes is a 180 Accubond pushed by a maximum load of Vihtavuori N560. I'm pushing an honest 3,100 over the chronograph and getting accuracy for the first three shots that hovers around 1/2 m.o.a. I've also shot this rifle and load at Vokes at 600 metres and stroked the V-Bull (using the third mildot), so I know it works for long range.
On the other hand, my hunting .30-06 is loaded with 168 TSXs and is also pushed by a max load of N560 for between 2,950 and 3,000 velocity. It also delivers about 1/2 m.o.a. for the first three shots out of my Rem 700 Stainless Mountain Rifle, but I've never shot it beyond 300. (However, at 300 yards, it absolutely flattened a large Muley near Williams Lake in '06.)
Here's the way I look at it:
For true long range hunting (where you want to feel confident that the rifle has the accuracy and ballistics to shoot at 500 or beyond) I'd go with a 180 Accubond. This bullet oozes ballistic coefficient and has proven long range accuracy to work way, way out there. At .300 Winchester Magnum velocities, this load will work for anything in North America, from 5 feet to 600 metres, assuming that you and the rifle/scope are up to the task.
I just don't have any experience of shooting the Barnes bullets at extreme ranges, so I'm not sure how they hold up way out there. Once you start shooting really long ranges, you'll soon realize that bullets that are superb, one-hole performers at 100 yards, sometimes don't shoot too well at 600. This is why competition bullets are designed the way they are. And the Accubond seems to be basically good enough to use as a competition bullet.
If you absolutely plan to keep your shots inside 500, then I think the 150 TSX or 168 TSX (or plastic tipped versions) would be outstanding. I like the idea of using the lighter bullets and being able to push them to velocities around 3,100. These would actually be very mellow loads in a .300 magnum, but give better performance than any .30-06, even a highly souped-up .30-06 like mine. Personally, I'm planning to eventually choose one of these bullets for the re-barreled P-14 I mentioned at the beginning of this post and load it to a velocity of between 3,000 to 3,100, if I can find accuracy there.
As to whether to go for a 130-grain bullet... that is an interesting idea. Personally, I'd shy away from it because sometimes .300 Mags can deliver questionable accuracy with super light bullets (all that blast pushing a little bullet through a 1-10 twist can create all kinds of interesting vibrations and stresses). In any event, I don't see the advantage of using such a light bullet. If you really want to shoot long range, the 180 Accubond is hard to beat, and all the extra velocity offered by a 130 won't add up to the ballistic coefficient advantage of the 180 Accubond. For lighter, general purpose loads with less recoil than conventional .300 mag loads, just go with the 150 or 168. It's easier to make these bullets shoot well in a .300 mag with conventional powders and pressures. But these are just my thoughts.
I'm also very intrigued by new 175 TTSX. I'd love to hear how it performs past 500. It could be in the running as the best all-around choice.