Dare I say it.... Its hard when you try, easier if you don't
Most people who cut pipe all day will get a straighter cut by eye, than trying to shoot for 90. If your consintrating too much on it, it seems your cut will drift more, while you try to fight it. 87 is acceptable, rather than wasting pipe, or worse backing up to re-aim an already started cut.
90 great, 87 fine, too much more than that you'll start to feel it when you pull, and thats a little unsettling.
As for the saws all I completely agree! I have a porter cable that just ripps pipe apart. I only use it for scrap and demo. For the stuff that actuall goes in, is done with a band saw.
Recently I saw on the supply house counter, a mini-bandsaw. Fantastic idea, I have been waiting for.... But, it was some wierd brand, and cordless, which means its toast when they fold, and it breaks.