Something that may be worth bearing in mind is that agents and publishers are running a business, and a busy and demanding one at that.
Therefore consider that any professional reading your manuscript is looking for excuses to put it down, so don't give that excuse - that means proper proof reading and editing where possible to get it as polished as reasonable.
Also, there's little point fretting over the amount of work that you send, because your work either stands out or says "dump me" on the first page. Therefore it won't matter if you've sent 5 pages or 50 - no one that busy is going to push through 20 pages of badly written and unappealing work and desperately want to read the other 30 you might have sent.
If, however, your first pages are great, the agent/publisher will ask for more as required, to see how consistent the writing is.
Just my personal opinion, because I remember fretting about similar things a few years ago, and these days think it's all kind of missing the point.
Just an opinionated couple of cents.
