Umm....the Slowounds and Prosteels are 2 completely different strings:
Slowounds:
-Nickel Plated Steel roundwounds
-Very smooth feel
-Very warm sound compared to most other nickel plated rounds
Prosteels:
-Stainless Steel roundwounds
-Fairly rough feel
-Bright with a piano string ring
For feel and sound, I'd say the Slowounds are much close to the standard D'Addario XL Nickelplated strings than the Prosteels.
Slowounds:
-Nickel Plated Steel roundwounds
-Very smooth feel
-Very warm sound compared to most other nickel plated rounds
Prosteels:
-Stainless Steel roundwounds
-Fairly rough feel
-Bright with a piano string ring
For feel and sound, I'd say the Slowounds are much close to the standard D'Addario XL Nickelplated strings than the Prosteels.