The 460 has almost twice the computing power of the 450. Until they are out and benchmarked we can't really know what that translates to in real world performance; but that's worth noting. Something really interesting is that the Radeon Pro 460 has almost identical raw graphics power as the GPU in the Playstation 4. (The Radeon 460 Pro has 1.85 TFlops and the PS4's custom GPU has 1.86 TFlops). That does NOT mean you'll get PS4 level gaming graphics at all; there's a LOT more to a GPU than simply the Teraflop value. But it does mean it's quite a stout mobile GPU. Because it's part of AMD's Pro line, it's going to be optimized more for applications like Photoshop, Maya or Final Cut Pro; rather than it is for gaming.
It also uses more power so you'll get reduced battery life when doing stuff that requires the GPU. Battery life will be the same for web browsing / basic productivity / streaming video / etc., because the integrated GPU which handles those tasks is the same.
For storage, I'd just look at your existing storage usage. How much do you use now? How much do you need? With USB-C and thunderbolt 3; you have a ton of options on storage. From big fast RAID arrays to still very fast AND very affordable USB-C (USB 3.0/3.1) external drives that can fit in your pocket and are bus powered. That $800 could easily go to external storage that can be used for large files like photos, videos, etc. IMHO, most folks purchasing a 15" MacBook Pro would only use the maxed out storage to store files like that. Unlike, say, a gaming laptop which would be chock full of software (games), that you really want stored on the internal SSD. That said; if you're willing to spend a little more than a USB-C drive, a thunderbolt SSD can be just as fast as the internal SSD, and could still save you a couple hundred bucks. I'd expect to spend around $500 on the fastest 512GB Thunderbolt 2 or 3 external SSD's. 512+512=1TB of course, and you're $300 ahead. That same $500 or so could also get you a couple terabytes worth of spinning disc external storage which is still suitable for working with most stuff.
Of course, if your pockets are super deep; there's no such thing as too much internal storage. Other than the price, there is no downside.
Of course! I'm with you 100% on the portability. Though I'm not backpacking across two continents with mine (too cool! Enjoy that trip!). But I do travel a bit for work and lug it around; I want my back as light as possible and my laptop to be light and portable too. Given that the 15" is about the same weight as the 13" I'm replacing, I'm sort of figuring I can fool myself into getting the power of a 15" that feels just as portable as my 13", even though I know the 13 would be more portable.
