Got a Penske fitted and running stock front end. Will probably switch to straight rate springs at first fluid change, but as of now not spending the $$$ on fork valving. That's always subject to change though!
FWIW, have GP forks on my FJR and they (or most any) are a marked improvement over stock when properly set up.
First I upgraded the rear shock spring to a 850# Eibach spring. Made a difference or but it is not an Ohlins or Penske.
Now have an Ohlins rear and .95 fork spring that I bought from SPS (So San Francisco). Both make a big difference. The forks still need a valve adjustment to get rid of the higher speed impact.
The rear alone is a HUGE upgrade, but it will also bring about the limits of the front.
I'd suggest you swap to proper springs up front at the same time. It's relatively cheap (springs are ~$85 and oil is ~$40) if you can do the work yourself.
I have the Ohlins on the rear and correct for my weight Sonic springs with 5w Motul in the front. The improvement was huge. You can always have the forks re-valved later.
Penske in the rear and .90 sonics up front.....Still a little harsh up front....Plan to send the forks to Nick for a rebuild and new valves when they are due for service...