In my opinion, the Heavy Fighter might look better if the lower engine wasn't on a strut, but rather connected to the bottom of the first engine. (to make it look less like a stiletto) Then you could remove the stubby wings on the lower engine and instead put those hardpoints on the bottom of the wings. Maybe make it a darker armor color to make it look more menacing, add in a different cockpit glass color (possibly dark red tint?), leave the menacing glass reinforcement bars (the criss crosses), and simply narrow the width of the nose? (not it's width up and down, but it's width from side to side, so it comes to more of a point.) The last thing that might be interesting to try would be elongating the rear facing 'fins' a little bit (like the original light fighter render), so they extend past the engine. Give it a more elegant, yet deadly look.
Xing - I think you said somewhere that you want to start work on an old project of yours again, the "Spikey Saber" originally meant for the Bundschuh. I think it would fit the Mandalorians pretty well.