I see nice improvement from 3GHz up (preamp on 10kHz BW), but I also see new spur at around 120MHz.
On a pics without preamp, you can see that spur at 120 MHz on stock (3kHz BW) is there , but on "post" 120MHz spur is 10 dBm higher.
Also new spurs at 1550 MHz and 2775MHz, 5-6 dBm..
Similar as "with preamp", from 3GHz up, noise floor is better..
It can be that now PSU buses became resonant on some (other than before) frequencies (lower ESR, higher Q), or probably RSA has some spur rejection in software that would need recalibration.......Or both...