It's not that Premiere is a poor quality program... however, it does have serious operational problems.
Adobe, including their after effects program and photoshop... by far their best programs... and I really can't argue the quality of those programs... but all of their programs are RAM hogs... especially concerning Premiere.
When it comes down to it... premiere is a great program for the price... and I can't argue the benefits of a semi-pro editing platform. But at the same time... an Avid system on your PC for the same price will give you much more bang for your buck... and on a Mac, it's FCP.
Lots of people love Premiere... but until they fix their programming issues, they're not going to accomplish anything except more of the same.
As for the blending issue...
Look into cropping the edges slightly... and feathering them.
However... the best way to accomplish this is to merge the images in production... matching one portion of an image to a portion of the other... so that you can blend them seemlessly...
Also, make sure the lighting & color conditions are the same.
Anyhow...
Good luck with Premiere... & good luck with the blend.
P.S. Look into the AVID forum for a full explanation of my personal dislikes when it comes to Premiere.