DG out of curiosity are you sponsored by Fanatec? Though they were hooking you up with some kit a little while back?
Housey, I'm with you on Oculus Rift, it sold me the first time I tried it, even with the lack of resolution it still far exceeds triples for me.
Here is how I would spend your £4k.
Rig:
http://www.h-engineering.net/shop/sim-rig-gt/
Personally I think this is the best off the shelf 8020 rig out there right now. HE are widely regarding in the Sim Racing community and supply many race teams. They also have possibly the best customer service I have ever personally received. It's been raced on by a GT3 champion (fitted with HE Ultimate pedals & a Leo Bodnar Sim Steering wheel/servo) Who loved it.
£1349 with the 8020 profiles.
Add your own seat, plenty to choose from that will fit your height/build, worth taking a trip and trying some out. Budget £250-400 for a decent seat but you could just as easily get something from a breakers yard if you desire. A friend has an old Porsche Boxter seat with the electrics all hooked up on his rig.
Pedals:
I would also take HE's Ultimate Pedals (or HE Pro's if you want to spend a little less on them/don't require up to 120kg braking force.
http://www.h-engineering.net/shop/sim-pedals-ultimate/
£1329
http://www.h-engineering.net/shop/sim-pedals-pro/
£719
This is a really good sim racing hardware review Chanel:
He also reviews the Bodnar Sim Steering, OSW & Accuforce wheels along with the HE Pro wheels.
Wheel:
You mentioned you have tried a Leo Bodnar Sim Steering, this is considered the gold standard for sim racing. From the components used, to the software and driving experience you really can't beat it but it's costly:
http://www.leobodnar.com/shop/index.php?main_page=index&cPath=101
Prices start at £2880 and that's without a wheel rim, pushing your budget too far (unless you want the best)
For almost 1/3 of the price you can still get a Direct drive wheel:
http://www.simracingbay.com/product/simucube-based-osw-kit-with-cm110-case/
I had one with almost these exact parts and I can tell you it was leagues ahead of anything by Fanatec/Thrustmaster or Logitech. There are forces you simply wont get with the other wheels like compression and aerodynamic forces, locking of the wheels under braking, it really is a huge leap and for me, it was worth every penny. I'm not sure the Bodnar wheel is almost 3x as good though. Sim racing Garage has excellent reviews and comparisons of Bodnar and OSW.
You'd still need a wheel rim with either option. I had a Sparco P310 custom made by Sam Maxwell
http://www.sammaxwellcustoms.com/gallery.php
Also consider Martin Ascher
http://www.ascher-racing.com/product-category/steering-wheels/
or Leopoldo Ramirez, who makes amazing replica wheels from real race cars if that's what you're looking for
You're probably looking at around £800-1300 for a completely custom rim, depending on spec etc, but if you don't require paddle shifters/buttons then there is a considerable saving there and you're looking at more like £250 with an adapter to fit the servo.
Shifter:
If you want H pattern shifter and don't want to spend £1.5k
http://www.pro-sim.co.uk/product-category/shifters/
Then I would buy The Fanatec ClubSport SQ. It also switches between sequential/H pattern with a simple switch and you can adjust the resistance to a shift.
https://www.fanatec.com/eu-en/shifters/clubsport-shifter-sq-eu.html
If you wanted sequential only then I would go with the Pro-Sim sequential
http://www.pro-sim.co.uk/product/psl-sequential-shifter/#tab-description
Pro Sim is owned and run by Adrian 'Quaife' Hobbs current GT3 driver and the same Quaife who make gearboxes/diffs. They've used technology from their sequential gearboxes to create their sim hardware. They're also a distributor for Leo Bodnar sim steering wheels.
Buttkickers:
I would certainly consider these, perhaps on in each corner of the rig and one of the underside of the pedal tray. I never owned them but had a couple of hours on a friends rig who does and they make a massive difference to what you feel.
As you've probably guessed by this point I'm quite passionate about all this stuff, DG is right that better hardware doesn't necessarily make you faster as such, but it was many many times more immersive/enjoyable for me with good hardware and felt the closest to a real driving experience as I have ever had, especially with VR. I've tried to recommend equipment on what I would choose based on what you've said your reasons are, and you could tailor things like the pedals and steering feedback to replicate the forces you would use in a real car/single seater racer.
If you have any other questions etc I'm happy to help.