I've used HPRP with my 3800 and haven't noticed any problems like this.
I'd be curious to know what would causes this "pizza wheel" issue.
Is it the paper? The FF loader? And why isn't it evident with other
satin/lustre papers such as Silver Rag?
The pizza wheel issue is caused by the little pronged wheels attached to the ejection rollers of the 3800. It only occurs when using the Auto Sheet Feed or the Rear Feed. It does NOT occur when using the Front Feed because when using the FF, the front ejection rollers are automatically lifted up and out of the way, so that the pronged "pizza" wheels do not actually touch the paper.
The actual marks are caused by these wheels digging into the printed sheet of paper (on the actual print surface area) before the ink has had time to dry. It is most visible in darker areas of the print, where the ink coverage is heavier (e.g., areas of solid black or near-black).
In general, softer papers (e.g., the Innova FibaPrint papers) are affected more than harder surfaces (e.g., RC papers such as Premium Luster). I assume this is because the softer surface allows the wheels to "dig in" more.
The pizza wheel issue actually affects all glossy/luster/semi-gloss papers -- any paper that takes the PK ink -- not just Photo Rag Pearl. It affects RC papers, Silver Rag, etc. -- to varying degrees. To see the problem, just aim a strong light at an angle to the print (e.g., a SoLux directional bulb) and tilt the print at various angles to the light. At certain angles, you ought to see the problem quite clearly.