I will tell you from experience that the weight is an issue. Anyone that installs one will know.. the 4l80e is almost 100lbs more in weight by itself...given using identical converters and such... My car obviously had more weight on the front wheels for a more nose tipped look after I installed mine. And I do have relatively new front springs on my car. The aftermarket crossmember will be heavier too.
More weight and a higher 1st gear can't make it "better" than a 2004r for performance.. but peace of mind does matter.
I have one in my car.. but don't really recommend it unless you really do have a low 10 sec or faster "street" car.