SSRS Report - TEMPDB VS INMemory

I am developing a 40 columns RDP SSRS report involves multiple tables ,more than 3 lakhs records and good numbers of calculative columns.

which is better approach TEMPDB or IN-Memory table?

Also i am trying to use RECORDINSERTLIST class in process method to insert bulk records

but Report is showing blank data,,,,

Help me!!

Thanks in advance..