Hi,
I have a F56 S and I'm seriously considering getting rid of it along with a Merc B250 4Matic and trade it for a Clubman JCW (no point in having 2 cars since both me and the lady are going to work from home) (thanks, 'rona, I guess...) and the difference in price between a new 2020 and a used 2018-2019 is substantial in terms of price (about 20k at least).
The question is: Can I take most of the performance difference with tune, intake and exhaust (cat back, I'm not willing to tamper with emissions), get it to about 5 sec 0-100km/h, 300 hp in an automatic pre 2020 one?

 

those are 2 different animals you’re considering. If it were me, I would go with the less expensive option and bolt on some parts to make it the driving experience you’re looking for. Unless you’re going to the drag strip, I’m not sure a practically modded ~ 250 hp car will feel that much worse to you. After mods you’ll have $10k+ in the bank for when ‘Rona ends and you need a second whip or some liquidity. JCW or not, the clubman doesn’t hold its value. If you’re sharing the car, Hopefully you’ve managed your wife’s expectations, the merc is a little fluffier then what you’re envisioning
as a build. Otherwise the second car will come sooner than you planned.

 

She doesn't mind even the F56 (in fact, she likes it!)
We're considering trading with a Clubman mainly because of 5 months of harsh winter that we have here and I worry about having a FWD lowish car as the only drive.
In fact, I only test drove the Clubman S and I found it a bit lethargic. I should find a 2018 JCW, test drive so I can gauge what to expect...

 

i live in eastern canada. Winters are barely habitable. The clubman all4 had no problem. It is a lot lethargic versus the coupe you’re hauling a lot more weight around. I put a tuning kit on mine and it helped a lot. The upgrades you are suggesting will improve the a acceleration. The JCW ride height is 10mm lower which isn’t great for heavy snow clearance or the crud in the wheel well. My wife has an x1 which is the same as the countryman as well, and normally lots available used but they hold their value better than the clubman.

 

My 2020 JCW Clubman was $40k with discount. You could probably match the acceleration with a tune. Personally my car is almost too fast, I can't really floor it or I'd crash it. But the rest of the car is also different from your car: the suspension, the tranny, the brakes, and All4. It's basically a BMW M135i with a Mini Clubman body (I think that's the one)