Sire T7FM vs Harley Benton Fusion-T: How much of a difference IS there? 

Same! I can only imagine how beautiful a Sire would look in that color.

Swapping pickups isn't too difficult so I tend to buy a guitar for the things I can't easily change (body/neck shape, fret types, etc). In this case, though, the Sire's pickups are much brighter than most humbuckers I've used, so I can see why it could be a dealbreaker for people less used to working with guitar electronics. But yes; when it comes to tone, subtracting what you don't want is much easier than trying to add back what doesn't exist! In the hand the Sire feels like a much better guitar than any of my Fenders. Fender makes good guitars, but the $1000 models feel like the $500 models from other brands. The Road Worn Fenders are the only ones that I'd take over a Sire, but that's comparing apples to oranges. At the end of the day, the best purchase is the one that makes you feel warm and fuzzy inside. If you buy a Sire thinking "I really wish I had a Fender..." you're better off just buying a Fender even if it doesn't check all the boxes. Also, remember that you can find used Fenders in like-new condition for basically half price! In the USA, I can usually can find exactly the model I want for way cheaper with 1-2 months of waiting. Keep an eye on Guitar Center's used inventory!!! Might make the decision a little easier. ;)

They're definitely not high output pickups; they're average for a humbucker.

I'll have to try that, I've been using the MusicNomad kit and it doesn't seem to cut it for stainless steel frets. Works well for regular frets though!