What's the difference? Does it matter which one I use on my 150k mile integ RS?

 

The High Mileage oil just has conditioners that help with seals and shiz. When it comes to conventional motor oil, it's pretty much like oil is oil. Different brands have different chemicals in them, but for the avid non ehusiast the cheap stuff is just as good as the slightly less cheap stuff. And changing the filter isn't totally nesassary with every oil change. Although I am going out on a limb here, and likely to get told differently. And I'm not recommending that you shirk on filters, but unless you really want the advantages of synthetic, I don't think oil that costs a dollar more a quart is gonna help or hurt either way very much.
I haven't heard of high mileage oil doing any harm as of yet.

 

does it matter...not really. i use valvoline high mileage just bc i like it. but do change your filter. and if you have synthetic stay with a synthetic oil.