Read
this post for a lot of answers regarding jargon and technical stuff.
Plastic will be much more reliable and easier to use for spares. Plastic is plastic, so pick one that you think looks good. You might hear some nonsense about "this ball is harder so it goes straighter" but it's bunk. Some are more expensive than others, but quality-wise they're all about the same. Plastic balls tend to last darn near forever.
Unless you have a good reason to use 13# stuff, I'd move up to 14# at least. Cutting your bowling from 5 games to 3 (typical leagues are 3 games) should offset any additional wear from a heavier ball. If the ball is properly fitted, you should be able to throw a heavier weight.
The BT Pearl has the same core as the Overtime and, according to Ebonite's website, is ever so slightly weaker than the Overtime. I don't think you'll see a significant difference in carry or pin action unless your style happens to match up better to a super-high-grit particle pearl verus a dull solid reactive. They'll give different reactions, but that's about it.
Of course, there's a certain thrill to getting new stuff (I call it New Ball Syndrome) that seems to make people bowl really well when they first get a new piece. And if it's cheap, there's no harm in getting it. Both would have a place in your bag.
SH
