I went through this exact dilemma before my trip to Iceland last year with my S5II, and I ended up getting the Panasonic Lumix S 24-105mm f4 Macro OIS. Honestly, it is the ultimate travel daily driver and I love it! Here is why I think you should go with it over the lighter Sigma:

• Dual IS is a game changer. The stabilization when paired with the S5II is absolutely mind-blowing. I shot sharp landscape photos handheld at half a second, which meant I could leave my heavy tripod in the hotel room most days.
• That 24mm wide end is essential. For dramatic landscape shots in places like the Highlands, 28mm just feels too tight. You will constantly wish you could zoom out just a tiny bit more to capture the scale.
• The macro capability is incredibly fun. It lets you get super close to details like moss, rocks, or flowers, adding a ton of variety to your travel album. Sure, it is heavier than the Sigma, but the build quality is fantastic and it balances really well on the S5II body. For hiking, just get a good camera clip and you wont even notice the weight!

> That 4mm difference on the wide end is kinda giving me second thoughts though since I do a lot of landscapes. I had this exact anxiety when planning a trip to the Swiss Alps! I ended up grabbing the Panasonic Lumix S 20-60mm f/3.5-5.6 and honestly, it totally blew me away. People sleep on this lens because it is often sold as a kit, but the optical formula is seriously impressive. You get two aspherical and three ED elements that control distortion and keep chromatic aberration basically non-existent, even wide open at 20mm. That extra width gives you a 94-degree field of view compared to just 84 degrees at 24mm. It makes a massive difference for big mountain shots! Plus it weighs a measly 350g. Yes, you lose some speed at the long end since it drops to f5.6, but for daytime hiking shots you will be shooting at f8 anyway. Love this little thing so much.

> That 4mm difference on the wide end is kinda giving me second thoughts though since I do a lot of landscapes. Late to the party but I am seriously obsessed with my current lightweight setup! I used to be exactly like you, obsessing over every single millimeter on the wide end. I spent years lugging around huge, heavy glass because I was terrified of missing that one epic landscape shot. But then I did a massive hiking trip and realized my gear was basically a boat anchor. It was honestly miserable! I totally get that anxiety about the 28mm, but what I found is that I actually enjoy shooting way more when I am not exhausted. I ended up grabbing the Sigma 28-70mm f2.8 DG DN Contemporary for my last big mountain trip and it was a total game changer for my back. The weight savings are absolutely insane! It feels like a feather compared to those big pro zooms. For those times when 28mm feels a bit tight, I just shoot a quick two-shot panorama and stitch it later. It works perfectly and honestly gives me even more detail to work with in post anyway. Plus, having that constant f/2.8 is a lifesaver for those moody, low-light forest shots you are definitely gonna find in the Highlands. I managed to find mine for a great price and it saved me a ton of cash for extra batteries and a better strap. Ngl, being light on your feet makes the whole experience so much more fun... you are gonna have such an amazing time out there!

Adding my two cents here because I have been hiking with L-mount gear for years. Honestly, dont trade reliability for a few grams. When you are out in the Highlands, the weather turns fast and you dont want to be swapping lenses in the rain or worrying about gear that feels too plasticky. I have tried many setups, but I always end up going back to the Sigma 24-70mm f2.8 DG DN II Art.

• It is built like a tank compared to those kit lenses.
• That f2.8 aperture is a lifesaver when the light dies down in the glens.
• In my experience, the weather sealing on the Art series is just a different league. Sure, it is a bit heavier, but that extra weight means it balances way better on the S5II body. I have seen too many friends regret taking the lightweight options when their gear fails or just misses focus in low contrast. Bring a good strap, pack smart, and just carry the better glass. Your back will get over it, but missed shots from bad gear stay with you.