saabcog, since he's talking about accelerating, heel-toe wouldn't really be used, but a double-clutch rev match would do the trick.
iDav, heel-toe downshifting is a pretty advanced maneuver, but it's a great skill to have; makes you a better & smoother driver, and it's way easier on your car.
I'm going to tell you to do an internet search to get full details and tips/instructions, but the gist of it is this:
It's a double-clutch rev match performed while braking... i.e., you're slowing down to approach a turn, and you want to shift into a lower gear so you can power through it without any coasting.
The basic steps are:
1. Right foot depresses the brake pedal to start slowing car.
2. Left foot depresses clutch pedal and shift lever is moved into neutral.
3. Left foot releases clutch.
4. While keeping toe pressure on brake pedal (maintaining deceleration), right heel rotates over to blip gas pedal to raise revs 1000-2000 rpms or so, depending on vehicle speed and number of gears you're skipping.
5. With right toe on brake and right heel keeping revs up on gas, left foot depresses clutch pedal and shift lever selects lower gear.
6. Left foot releases clutch, right heel comes off gas pedal pretty much simultaneously.
7. You are now engaged in your lower gear, and can transition off the brake and onto the throttle as usual, making your way through the turn with much more speed and control than you would've done otherwise.
8. Your friends in the car praise you for your serious driving skills. Hot chicks are waiting anxiously for you at your destination.
EDIT: reading through the thread again, I should clarify -
iDav, the double-clutch and heel-toe stuff I described above, those are both downshifting techniques... like if you were already in 5th and wanted to punch it in a lower gear to accelerate faster, or the heel-toe deceleration scenario I described.
In your original question, I understand it as you're accelerating hard from a lower speed... so you're only upshifting. In that case, neither of the above techniques would come into play.
My thoughts are pretty much that when you shift more slowly, you're essentially holding the car at steady throttle until the turbo is completely spooled up and ready to dump full boost immediately, whereas on your hard acceleration right after the shift, the turbo has had time to slow down, so you're asking for full throttle right off the bat... and the first couple seconds of that will be spent spinning the turbo up.
As far as letting the driveline slow down to match the wheel speed, I don't believe it'd be a factor once the clutch is let back out (except in terms of driveline strain). There is a remedy though, that would improve the smoothness of those fast shifts - you could install a lightweight flywheel. The car will be a bit more touchy, but those revs will fall faster, so you can perform a rev-matched upshift in less time than stock.