Testing conditions:This does seem close, if both were connected to dummy loads there would still be ample signal pickup.
Result of FST4W-300:With a recommended maximum of 0.56Hz for -300 this is quite possible.
The HF+ is quite stable in the short term when warmed up. Using software like Spectrum Lab you can monitor frequency very precisely.
I am not convinced there is any need to use FST4W on the higher frequencies but there may be times that there is an advantage.
73 Alan G4ZFQ