To be fair, T-Mobile's CEO isn't doing its network any favors by specifically saying, more or less "Come at me, bro" to heavy users. And by offering a reference point price-wise to unlimited at 4.5GB, you're effectively guaranteeing that your average $70 per month customer (less if they're multi-line) is hitting 5GB per month. And, let's face it, for all the whiz-bang-ness that is DC-HSPA+, it's about half as efficient as LTE, less so on the upload side.
Here in Austin, we're less than a month from T-Mobile LTE getting deployed (I have a source outside TmoNews), and their network consistently performs better on the download side than Verizon LTE, as long as you've got reception of something better than EDGE. Heck, uploads aren't too far off either; in the Sprint store at 360 and 183 in Austin today I hit 7/3 for Verizon, ~22/1.5 for T-Mobile and couldn't quite get a solid LTE signal from Sprint yet (I'll bet said solid signal is less than three weeks away, at which point I'll see 15/5 or so). But...and this is a big caveat...I spent multiple hours in EDGE-land because H+ building penetration isn't all that it's cracked up to be. And EDGE on T-Mobile is pitifully slow when you've got indoor coverage issues in places where people are likely to be checking their phones.
When LTE goes live, I'm reflashing the baseband on my Nexus 4 back to the version that allows AWS LTE, since I'm sure latency will be slightly lower (I've seen 22ms on H+ before though!) and upload speeds higher than DC-H+. But I fully expect my phone to be waffling between LTE and H+ (and in some cases EDGE) more than a Denny's chef on a Saturday mid-morning.
As an aside, T-Mobile has plenty of spectrum in PCS and AWS with the MetroPCS merger...in some cases they have as much AWS alone as Sprint has PCS A-G...plus T-Mobile has PCS on top of that. But, as AJ has said, T-Mobile has made the questionable decision of putting the more fragile airlink on the more fragile spectrum (at least for now...give them three years and watch 'em put LTE on PCS), with no low-frequency backup. Reasonably good in urban environments, and lightning-fast when they get 20x20 online, but T-Mobile needs 600MHz spectrum more than anyone at this point, and that's one thing that MetroPCS won't give them. But maybe they can just focus on cities and roam on Sprint for rural coverage...nah, that'll never happen until the two merge down the line.