Definitely the better lens is better! The real question is whether the difference is important to you. Even though the slower lens gets sharper when stopped down it never becomes as sharp as the 24-70mm F/2.8 wide open and the difference becomes even more significant with the F/2.8 stopped down.

• Sharpness would be the first reason. While lens sharpness can be measured scientifically, once details are scaled into a certain print size or online image size, the perceived difference diminish or disappear.

There are way more reasons to get the 24-70mm F/2.8 than sharpness. This lens is better build and this means you can count on it more and it can handle rougher treatment. This lens is also weatherproof which lets you use it when it is raining or snowing. As a professional, you often need to keep shooting regardless of the weather and so having equipment that stands the elements is pretty much required.

• Weatherproofing is the second reason: Do you go home when it rains or snows, or there is incoming sandstorm? Once I was with a group in Peu on the world's highest sand dunes and people took their cameras out when we reach the summit. In under 15s a Canon EOS Rebel and Powershot died. The fine sand entered in the unsealed lens barrels and ever movement of the lens or AF had so sound me sand scraping metal inside the lens barrel. My while mutli-coated polarizer was very scratch, my Pentax DSLR, a K-5 just need a rince under the faucet to clean it up but it never stopped working

Travel photographers in particular are very specific about equipment choice because versatility is key. Weight and size limits what you can have available and so we tend to choose more versatile gear, so even if there is another lens that can take better or equally well a particular photo, other photos on the same trip must also be considered when choosing what gear to carry. Lens selection for travel photography requires careful planning and I can say that it often takes me hours or days to decide on which lens to take and I usually work back from those to figure out which cameras, plus all carry-on and hand-luggage restrictions need to be checked against that selection, so I often have to refine it. Of course, sometimes we are required to take certain gear and in that case then I have to figure which one to complement the gear provided by the manufacturer.

• Versatility a great reason: After you take those forest shots at F/8, do you intend to go get the heavier lens before heading to the next place? What if on they way back in low-light, we see something your cheaper lens is too slow.

The best advice I can give is buy the best gear you can afford if you cannot buy it all. Top-gear lasts very long and so you will generally get very good use out of it but cheap gear will most likely be sold at a least when you want to upgrade. My new moto is:

Strive to have fewer better things!

Just apply this using your own definition of better.