OK, sounds like your factory barrel is good and there's reason to have a bit of confidence in that assessment. Maybe it is worth spending a bit of money on it.
The American approach to Palma reamer design is towards a very short throat. This started when one had to shoot host-country supplied ammo, which used the old Sierra 155 (#2155) bullet, seated nominally to magazine length but usually in practice 2.775"-2.790". The "Warner 95 Palma" is one such design; at one rifle measuring session I seem to recall a Warner-95 chambered rifle needing to have a bullet seated .032" deeper in the case than my JGS .308 Obermayer chamber (and the 308 Obermayer is already a short-ish throat design).
I am not sure where the 2011 Kiff/Gamboa/Flaharty reamer that you show fits in the scheme of things (though my guess is that it would be a typically short American design). The print indicates a leade dimension of .050" but I don't offhand know that dimension on a Warner 95 Palma or on a 308 Obermayer, and I was a bit surprised that I couldn't find it with a quick Google search.
The nose on the Sierra #2156 is quite long (it's a long way in front of the driving band). Even with a very short leade such as the Warner 95 (and possibly/probably also the 2011 Palma reamer you are considering), you might not be able to get the bullet to touch the leade with a COAL of 2.860" (your max mag. length is 2.845", I'm adding another .015" as a likely amount of jump you'd want to use and would be happy with). The most efficient way to answer your question is to find any Palma shooter who has a gun chambered with that ream and who shoots Sierra #2156s; I would imagine that would be a pretty common combination in the US. Or, phone Dave Kiff or Dennis Flaharty or Bob Gamboa and just ask them, this is something they'd know off the top of their heads.
The Berger 168 you are considering is about .020" better in this department than the Sierra #2156. This might be just enough to help you out, but it might not be. Oftentimes the Berger VLD designs are quite finicky in load development, so this would be a relatively risky combination to try (since your fixed magazine length limit will tie one of your hands behind your back).
Using a shorter-nosed bullet, or a more jump-tolerant bullet, might be necessary. Some ones to consider:
- Lapua 155. A finicky bullet, but very high quality and high performance. Short nose design. Might work with your chamber as-is. If not and you need to rechamber, it would need a reamer with a throat much longer (about .0.150" to 0.200" longer) than the one you are considering.
- Berger 155.5 Fullbore. A long nose bullet, but very forgiving and jump-tolerant. Might handle your chamber as is. Will work superbly with the 2011 Palma reamer you are considering.
- old Sierra 155 #2155. The original Palma bullet, now one of the lowest-performance 155s on the market but still just as good / the same as it always was. Quite a short nose. More jump-tolerant than the newer #2156 but I would not bother trying it in the long factory chamber you have.
- Sierra 190 Match King. Would need to be loaded to about 3.050" COAL to touch your lands in your factory chamber, however it might be jump-tolerant enough to deal with being seated to magazine length. Probably not your best choice though.
- Sierra 175 Match King. Shorter nose and quite jump tolerant (I *think* it's the same nose as a 168SMK). Essentially it's just a SMK168 with a better boattail (and it doesn't suffer from the SMK168's dynamic instability that kicks in at longer range). However well magazine-length 168SMKs work in your rifle today, is about how you can reasonably expect 175SMKs to work in your rifle today. It would also work very well in the 2011 Palma chamber you are considering.
A lot of this is a time/money/effort tradeoff. If you are short on time but have a enough money to spare, the no-brainer approach is to buy any of the great match barrels our there (Krieger, Bartlein, etc...), in the profile and length of your choice. Choose a bullet or class of bullets you wish to shoot. Select the reamer accordingly (if necessary it's easy to get a custom one made), and get this installed on your receiver. Chances of superb results the first go round are more than 95%.
If you are short on money, or if you have plenty of money but would enjoy the testing & trials associated with finding a bullet or load to fit what you currently have or are able to cheaply modify, then you should go ahead and play with what you have (either do nothing to the gun and see if you can find a bullet that works with it as-is, or rechamber the factory barrel as you suggest).
