I assume these are ‘Evolution series’ Fox 32’s if they came as OEM spec on your bike.
I’ve owned a couple of pairs of ‘Performance series’ spec 32’s with the O/B damper. Like all forks you obviously have to keep on top of servicing to keep them feeling their best.
I found them perfectly fine for local woodland single track riding. But if you start doing anything too aggressive with them then their limited performance does really start to show.
I wouldn’t bother going down the upgrade route. Nothing wrong with the FIT damper. But if you want better performance I’d take that £330 along with the £100 service and what every you can sell yours for accurately described forks for and buy a completely new fork.