I just got the T-mobile SIM through Straight Talk a couple days ago. I'm very pleased. I switched from T-mobile's $50 prepaid plan because it throttles you to 2G after 100 MB. I was unaware of this restriction on Straight Talk's plans... considering they advertise unlimited data with no restrictions.
If I'm streaming music (which I often do) I go well over these amounts. I fully expect to now pretty regularly now that I've got my Ingress invite.
I'll let you know what my experience is like.