1 GB memory vs. 1.5 GB in Macbook?

Ok, I thought it was about time to ask my first question (yay!)

Anyway, I finally decided to upgrade the memory in my mid-2007 Macbook. It originally had 1 GB (2×512), and I’ve decided to upgrade to 2 GB (2×1GB). My mom just upgraded her laptop, and had one extra 1GB stick that happened to work with my laptop. In the meantime while I save up for 2 Gb (yeah, I know it’s not that much money, but I’m broke after buying Christmas gifts and, ya know, being a college student and all that), I decided to throw the 1 GB stick in there to get up to 1.5.

So, here’s my question. I know that memory isn’t as effective with mismatched sticks vs. matched sticks. Would matched sticks equaling 1GB be more effective than mismatched sticks adding up to 1.5GB? Or does it really not make a significant difference?

Sorry for being long-winded, but I wanted to give all the relevant details. Thanks in advance!