Lost track but looks like you might have gotten two sears and MP5s? In which case one should be come a MP5K-PDW and the second sear moved to full time 5.56 .... LOL!
I picked up a MM53 with a RCM barrel for near two grand nearly two years ago, that shoots nice and the receiver fits a lot nicer than the Vector ;-). I like the full size MP5, the MP5K-PDW, the "HK"33K (friend has it now as was not being used with the MM23eK as much) and the "HK"53 (really a must have with the MP5 ;-) along with something in 308, be that a G3K, HK91 or the "HK"11 (quick change barrel and $4K now days for one from MM). Count the "HK"51 ane "HK"53K more as subguns to go with the MP5 40 or 10mm .....
The MM11 or MM13 are a third of the cost of the belt fed guns and really make an interesting off hand option that also works as a near light machinegun with a drum mag. Plus if you have a second barrel can use one for heavy full auto and keep the second for a more accurate rifle, but I am repeating myself mostly since that is what I am looking at currently, just would like shooting one off hand to see how the weight is (the MM23eK holds nice off hand but is none too light for an old guy like me ;-).
Was looking at a G3K and then a MM11K to go with my MM23eK. Other option is replace the G33K (friend go) and the HK93 with a MM13K, so would have the MM53, MM13K and MM23eK ... but this is long term thoughts and for now get buy fine with the MM53, HK93 and MM23eK ;-).
http://www.556beltfed.com