So I thought about this a while back. I knew there was almost every possible combination of notes avaliable in dominant 7 chords.
You can have 9 b9 b13 13 6 11 #11 ect... But something I didn't think about was the possiblility of a major seven with in a dominant seven chord. I asked about it on Yahoo Answers, sure enough, I got some stupid sterio close-minded answer that there was no such thing and something like that would have no use. But I was writing a song and bam, the chord was used my accident and sounded fantastic and tense. The chord was a (I hope you can read chord symbols) G7#5#9(maj7) Which for those who can't read that means you have a G7 chord but the 5th if sharped with a sharp nine and a normal f# which is the major seven is added with the dominant seven chord. Here's the line I used it in the key of Eb: Eb - G7#5#9(maj7) - Cm - Bmaj7b5 Very Jazzy-Bluesy line right there :D

Well, I haven't seen such a chord yet, but if it sounds good to you, then why not using it?

so essentially what you've done is a G7 superimposed with an Eb min. Am I right?

so essentially what you've done is a G7 superimposed with an Eb min. Am I right? Your talking about playing a G and F in the Left hand over a Ebm? Yes but it's kind of like a Bmaj7/G7 I suppose because it spaces the 9 and #9 better than having a triad in the left hand, but that may work too. It works well as a substitution for a Bmaj7b5 chord. :sweat: