Stage 2 Octavia Mk2 VRS clutch slipping?

Two months back I bought a 2009 TFSI VRS Octavia manual. Stage 2 Revo remapped in 2011. Huge stack of paperwork with the car, and it looks well cared for. The car has various other upgrades eg. ITG Maxogen intake, R32 brakes, Audi tt rs short shifter, Milltek exhaust etc. Serviced religiously. Revo have told me it's likely to be around 260hp on high octane fuel, which I do use. 

The car is on 109k miles, and seems to have had three (!) Sachs organic clutches...so far. Gulp. 

Within the last week as I push the accelerator in gears 3-6 the revs jump, then settle down again, and with less aggressive pedal, the speed and revs climb as normal. The car also revs on hills, but the power isn't there. The clutch has always been tough to push down but I'd put that down to it being a heavy duty clutch. I'm assuming it is the clutch slipping, but the car had a new one in 2019, along with a dmfw. 

The cars had a whistle from the engine bay on acceleration which I had assumed (not being a modified car guy until now) was just part and parcel of the tuning / normal turbo noise, but maybe it's a split pipe. 

Any suggestions on what clutch I should be fitting, and why it's eating clutches...

And if you'd just gambled on an ancient modified VRS TFSI, what should I be saving up for / having sorted as a preventative measure?