Either way won't be much of a difference in speed.
I have 2gb in my Imac and have quite a few apps open and it is quite fast. Don't often hit the limit. Even have 4gb sitting here in its packaging and haven't seen a need to install it yet.
Having a SSD improves the biggest bottleneck and in the MBA that is taken care of no matter which model you choose.
When your programs launch in a second or two from the SSD then it doesn't matter much if it wasn't in memory to begin with and has to be paged into memory from the SSD.