Hmm I never understood(and still don't understand) what an RPC node is, but your bit about the default nodes being slow due to heavy load makes sense.
I actually made a script a few weeks ago using the steem-python api, and it was REALLY slow, until now I thought that the python api itself is slower than the other APIs, but after reading this post I realised that its the RPC nodes.
You should give it a try with another rpc node and see how it goes.
Depending on the complexity and number of queries it can make a big difference