I had a lot of foil/PWW resistors, including Vishay HS BMF types and old russian S5-27, S5-53, S5-54, S5-60, S5-61, R2-67 e.t.c. Moreover, through my hands have passed hundreds of such resistors. IMHO, the S5-61 type 5 have the same long-term performance, as VPG hermetically sealed types. The most stable LTZ-based voltage references, I made, have a statistical 10:7 voltage divider with S5-61 and gives less than 1 ppm/year drift rate.