Some questions about Sony DRU-800A and media

I recently purchased my first DVD burner - Sony DRU-800A. With my burner, I purchased Fujifilm 8x +Rs and -Rs. The +Rs being YUDEN000-T02 and the -Rs being TYG02. In viewing the media write strategies in the 800A firmware, the +Rs are rated from 6x - 8x and the -Rs are rated from 4x to 8x. I had already burned a couple DVDs before I learned this information which leads me to my first question. Is it okay/safe to burn the +Rs at 4x or less, or would I get better burns at 6x or 8x?

Also, I’ve come to find out that -Rs burned by my 800A do not play in my standalone DVD player but do in my brother’s. This, I don’t understand. I have other -Rs from friends that play fine in my DVD player. Why would their -Rs work and mine not? The +Rs burned with the 800A play just fine in my DVD player. I’ve attached the quality test results of the +Rs. I’m new to PI Errors and PI Failures and don’t fully understand what I’m looking at. Any help would be greatly appreciated. Thanks.

The Disc Quality scans are all right.
However it seems to me that there’s too much PIF…
Anyway, this shouldn’t be an issue.
You should try setting the book type of DVD+R to DVD-ROM. You can do it by a program called BookType Utility - it can be found here.

Why would I want to change the book type if I’m having no problems with +Rs?