The KEF flights aren't real PS as they use older 757 aircraft (without any D1 flat beds) where PS is sold as the top cabin now. IIRC some of these flights have breakfast as their only meal.

For DL PS flights, look for A350 and 777 aircraft routes (with suites). All A350s are brand new and equipped this way, while the 777 fleet is currently in the process of being reconfigured with a PS cabin. There's a big thread in the DL forum discussing particular tail numbers and the progress on this.

The DL PS dinner service seems to be a choice of the chicken or pasta main courses from the D1 menu (same food, but two rather than four choices, with fish and red meat selections missing). There's a menu and the wine is better than DL domestic FC but not as good as D1.

Unfortunately DL no longer is granting lounge access on the basis to a PS ticket, nor are PS passengers normally given domestic FC seats on connecting flights when a through PS fare is used, although there might be a few exceptions for full fare classes. Some PS fares aren't more than certain coach fares while you sometimes find a RT advanced purchase Z fare for D1 that isn't much more than PS would cost.