Hello and welcome. 500kb-1mb is usually a good range for full-page mag scans. The print quality in Penthouse was never great so there's nothing to be gained from attempting higher resolution. I compared your scans against my hard copy and I'd say your colors are slightly under-saturated but this is very minor. I'd say your scans look very good overall; they're certainly better than my early efforts. Please scan and post full pages. Those of us who collect magazines appreciate this.
This particular pictorial has already been posted
here by some character. This was one of my earlier scans and as you can see the quality is lacking. We have a rule against duplicate posting but your scans would be allowed in this case because they would be an upgrade.
I hope this is helpful and feel free to PM me if I can help further.