The OP is right, Sprint 3G speeds are equivalent to AT&T Edge speed, and Sprint 4G speeds are equivalent to AT&T 3G speeds.
If you rely on 3G speeds a lot, you're better off going to AT&T or T-Mobile. Verizon 3G speeds are not that great either.
With Sprint, you cannot use your own experience to project to anybody else. It is just inconsistent. You have people saying Sprint is really slow and other saying Sprint is fine. They are both right, for their areas. Michigan in general is very bad. In my area, at the local mall I get 1.7M/850k. At my home I get 350-550k/250-450k. Roaming on VZ at my home I get 2.2M/950k. This is all with the same phone. So is it really slow? yes, is it reasonably fast? yes.
All that you really care is how it performs for your own situation. If it is slow everywhere you use it, then you should return it. It could take many months before it improves and there are no guarantees. However don't make the assumption the network performs that slow everywhere as there are areas where it works fine.
As to PRL, if you are talking native Sprint, it is highly doubtful it will make any difference. The Sprint native portions of the PRL haven't changed in ages, only the roaming partners.
As to signal strength, it can make a big difference if you have low signal strength when you are testing. I know a coupld of people who upgraded from Evo to Evo Shift and Evo 3d who are getting slower speeds than there Evo due to signal strength as tested with side-by-side comparisons. However, if that is the primary location you use your phone and you can't move around, then it doesn't matter if at the window you can get acceptable speeds. Don't expect the signal strength to improve until they finish their network vision upgrades and even then, there are no guarantees. Go with what you know, rather than what you are promised. Once again, if it doesn't work for you, return it. If it turns out the Epic Touch has poor radio performance, you might want to try out a Photon, which has the best signal performance of any Sprint phone right now. Of course, if that isn't a phone you want, once gain, Sprint doesn't work for you, so get out.
As to 4g, people were getting 6-12Mbps when it was first released, but now that more people are using it, it is often down to 2-5Mbps. There is always the potential for this to happen to any carrier as more people use the network and the backhaul is exhausted. WiMax is clearly capable of handling faster speeds so the bottleneck is somewhere else. Again, if you have slow speeds in your area making it unusable, return and get out.
Sprint changed their return policy from 30 days to 14 days starting with purchases 9/16/2011 so if you want to return it, do it soon, don't dither around trying to give them a chance.
Having said all that, there are many areas that Sprint works ok. so it doesn't help trying to convince those folks that Sprint is unusable. It just isn't true for them even though it might be true for you.