Recommended BPM Context size

Hi Experts,

Lately, I have been reading about BPM performance and came across a recommendation which advice to keep the BPM Context size to minimum possible in order to avoid performance issues. I have following doubts on this -

1. On an average, what should be the limit of context elements count to avoid performance hit? 20-30, 60-70, 90-100 or more than that?

2. By mapping the context with reporting data-source, would it be possible to transfer the data burden to reporting data-source?

We are currently on PO 7.4.

Thanks.