I'd wish to apologise for the rant in advance, so if you think that I post crap most of the time, don't bother reading on!
So, let me get this right. You have a car which is stunning to look at, great to drive and shiny new to you, and you want to spend time and money on loosing perhaps upto 50kg to make it quicker? Going off online (read optimistic!) 1/4 mile calculators you will gain 0.1 sec 0-60 take less than 0.1 sec less to do a 1/4 mile and have a 1 mph higher terminal speed, so it is hardly going to be noticeably quicker. I apologise if you are a driving legend and can launch your car off the line repeatably to within 0.1 sec of it's optimum, and are always in the right gear for the right bend on the right line with no other external influences, such as other traffic on the road or track, can guarantee ideal road conditions, etc. but if you are not all of these and do live in a world where reality does get in the way, what would be the point? £5k is ~18.5k miles of fuel! (at 20mpg, £1.20 per l), what could be a better use of that time and money than that?!
Are you going to look back on your ownership and say, "Well, that trip through the Evo triangle would have been so much better if I had gun drilled my driveshafts and waxed my chest hair off to save a bit of weight..." Or are you going to say, "Damn, I wish I'd been here in the Seven when I had it, it would have been epic..."
Personally I'd nail in a comfy seat (or padding) and spend the time and money smoking the 🙆🏻 off it visiting all the great roads and places that are possible.
BB