"2010 macbook pro… Is it better to have two 4GB cards or one 8GB with one 2GB card?"
The SSD does not matter. All i5 and i7 processor Mid 2010 models are limited to 8GB of memory, so it won't start at all with 10GB. Therefore, in the case of i5 or i7, the 8GB configuration will be faster by years.
For Core 2 Duo processor models, the limit is 16GB based on owner reports. You may be able to find a one second difference in a two minute task when using 10GB compared with 8GB, but I doubt it.
You should probably keep the ram even in terms of the amount per slot. Also, 10 would not give you a noticeable difference over 8 with your laptop. I would go with the 4 and 4.
It will only see (and use 8GB) so there is no point in putting more in.
" I can get it down to 500mb left "
That is not how it works….
They must be balanced.