I've had the issue for a while. In my case my instance was hosted in San Mateo, whilst I was in Europe. So 9 hours earlier. At night (San Mateo time) Marketo and RCE sync the data, putting strain on both systems. But night time in San Matea is my morning in Europe! So in Europe it was slow till lunch. In the afternoon it was much better. It was on my roadmap to have it migrated to Europe. Maybe this applies to you too.
Thanks for the information, I find it slow generally, will certainly test it out at different time, though I tried at the weekend and it still slow, how do I know where my Marketo instance is hosted?
Your regular Marketo instance location can be seen in the URL. If you see app-sj, it's in San Jose. app-ab is Ashburn, app-lon is London, etc.
I believe, though, that almost all RCA instances are in the US. It's not necessarily the same location as your Marketo instance because it's a separate data warehouse.
It also hugely depends on the size of your database. We've been told RCE reports don't work (or have very limited functionality) if your database exceeds 1M, which makes it unusable for us. Apparently improvements are coming in Q2, so hopefully that helps.