Strictly in my opinion, this kit is fantastic. It provides ample damping without ever crossing the line into harshness. The feel that the front end delivers is very good - certainly on par with a top-shelf sportbike fork. The rub? It's still nonadjustable for compression. So, it's like finding a sweet spot/setting...and leaving it alone. In theory, you can adjust the shim stack to change the compression. But realistically, no one is going to do that. So, there are some compromises for changing road conditions, ambient temperatures, load, etc. over a fully adjustable setup.
The heavier fork springs and oil are a great budget solution for the bike, but the results are pretty vanilla when compared to the FPK or other performance fork work. The heavier oil allows the stock internals to develop more damping, but it comes at the expense of more high speed compression damping. On smooth roads, this is manageable. On roads riddled with frost heaves, cracks, or otherwise uneven surfaces, it can be a bit jarring (for my tastes and pace).
When a customer calls, I give the same spiel: The 8900E and heavier springs/oil 'fixes' the bike. It reduces the see-saw effect and eliminates the pogo'ing. Gaining the proper spring rate reduces dive/squat and allows the bike to work for the rider. Having tasted each iteration one at a time, this is what I'll call the bare minimum solution. At under $750, you get a sorted suspension that works.
The 8983 or 8987, and now the FPK, falls under the performance modification category. One ride back to back and it's clear that the money you spent went somewhere....and somewhere good.
But to (finally) answer your question, it really comes down your budget and expectations. IMO, yes, nearly all riders can appreciate the level of performance afforded by the FPK over a set of heavier springs and oil. It all comes down to wheel control and having the suspension work with you, not against you. Unless you're droning down a smooth highway, this kit's improvement is a noticeable, and welcome, improvement. You don't realize how little your wheel follows surface irregularities until you ride a properly set up suspension...the wheels follow the the road, and the end result is more traction and control. I mentioned this in the build thread, but I'll repeat it here for this audience. I was very pleasantly surprised with the performance of this kit. I went into it expecting to take it back apart and re-shim the high-speed. That simply wasn't the case - Barry @ GP did a great job on the stack. Knowing what I know, I shouldn't have doubted the results. But for the money, you can't go wrong.
Time to start saving. BTW, if anyone is looking for an almost new set of Sonic .85 springs, they'll be up for sale as soon as Nick's 25mm kit comes up for sale.
