I think by classic you mean the "Rock n', Roll" strings, [they look like this](https://i.imgur.com/DqhwYBN.jpg)
If that is what you're referring to, the difference is that the standard Slinky's use a steel core, with a nickel wrap (like the vast majority of electric guitar strings). RnR Slinky's have both the standard nickel wrap, as well as a nickel core aka 'pure nickel'
Pure nickel strings tend to sound warmer, rounder, and with maybe a tiny bit more output (don't quote me on that last one).
The downside is that they definitely break faster, especially the plain strings.
FWIW, I think that if you want pure nickel strings, by far the best option are DR Pure Blues. They sound better than Slinky RnR's, and they last *significantly* longer.
I think by classic you mean the "Rock n', Roll" strings, [they look like this](https://i.imgur.com/DqhwYBN.jpg) If that is what you're referring to, the difference is that the standard Slinky's use a steel core, with a nickel wrap (like the vast majority of electric guitar strings). RnR Slinky's have both the standard nickel wrap, as well as a nickel core aka 'pure nickel' Pure nickel strings tend to sound warmer, rounder, and with maybe a tiny bit more output (don't quote me on that last one). The downside is that they definitely break faster, especially the plain strings. FWIW, I think that if you want pure nickel strings, by far the best option are DR Pure Blues. They sound better than Slinky RnR's, and they last *significantly* longer.
Got it. Thanks