Recommended 4g speeds

I want to switch networks, VF is working fine for me, but I'm paying over the odds for my usage. I got a sim card from iD and coverage seems to be good, but I've noticed that the 4g speeds I get from them are consistently about half what I get on VF. What I don't know is if the iD speeds are going to be a hindrance or anything. The handset I'm using for the iD card is too old to prove useful to me every day, and I don't want to put the sim into my current phone as my number hasn't been changed over.

What I really need is some sort of chart that says "if you (x), you need (y) mb/s", with things like email, browse, facebook, etc. I realise in this day and age, I can simply swap over my number, and move on after 30 days if it's not suitable, which I just might do, but it'd be nice to know my limits anyway.