I made some assumptions here... the key assumption is that with either launcher type, you need 120 hits within a 10 second period to trigger a shockwave. (from the Battle Pirates Wiki) I also assumed a 0.1 second delay between shots within a salvo. The other simplification I made is that no hits or damage is wasted (no overkill, no firing at dead targets).
For my calculator inputs, I take into account three general areas: the Weapon, Attacker, and Defender.
Weapon: I use the statistics from the game, and also document the assumption that you need 120 hits in a 10 second period to start generating shockwaves. If you want to try other assumptions or statistics, go ahead.
Attacker: In this area, the number of launchers used, the attacker's reload bonus, and the attacker's accuracy bonus (or penalty) should be entered.
Defender: In this area, select "Y" for a ship target, or a "N" for a building target. The evade and Radioactive Defense percentages should be entered as well.
The outputs are as follows:
Net Accuracy (NA): This is the percentage of shots that are expected to hit, given the target type, accuracy, accuracy bonus, and evade. NA = Accuracy * ( 1 + Accuracy Bonus) * (1  Evade)
Net Reload Time (NRT): This is the total time between the end of one salvo to the start of the next salvo. NRT = Reload Time / (1 + Reload Bonus)
Net Damage Per Hit (NDPH): This account for the target type, salvo number, and resistance. NDPH = (Damage * (1Defense)) / Salvo
Number of Launchers (NL): (from the attacker area)
Launcher Weight (LW): Number of launchers times weight per launcher  lets you compare total weight.
Hits per Second (HPS): Average number of shots expected to hit the target per second HPS = NL * (NA * salvo) / (NRT + salvo delay * (salvo 1))
HPS/hton: (HPS / total weapon weight) * 100
No Shock Damage Per Second (NSDPS): The weapon DPS without any shockwaves. NSDPS = HPS * NDPH
NSDPS/hton: (NSDPS / total weapon weight) * 100
Shockwaves per second (SHpS): Given the number of hits per second, the average number of shockwaves generated per second. If the average time to generate a shockwave is longer than the Shockwave Threshold time (10 seconds), this number goes to zero. SHpS = HPS / Hits to shockwave (unless less than 1 / Shockwave Threshold Time)
SHpS/hton: (SHpS / total weapon weight) * 100
Shock DPS: DPS from the shockwaves only. Shock DPS = SHpS * Shockwave Damage * (1  Defense)
Shock DPS/hton: (Shock DPS / total weapon weight) * 100
Total DPS: No Shock DPS + Shock DPS
Total DPS/hton: (Total DPS / total weapon weight) * 100
So here's some example scenarios with enough launchers to ensure shockwaves:
Reload Bonus

Accuracy Bonus

Evade
 total DPS/hton  
D92U  D92F  D92F DPS Margin  
0%  0%  0%  20.53  27.07  32% 
50%  0%  0%  29.23  36.21  24% 
100%  0%  0%  37.09  43.57  17% 
150%  0%  0%  44.22  49.63  12% 
100%  20%  0%  29.67  34.86  17% 
100%  35%  0%  50.07  58.82  17% 
100%  35%  20%  60.09  70.59  17% 
100%  35%  20%  40.06  47.06  17% 
100%  35%  50%  25.04  29.41  17% 
25%  0%  Building  28.94  57.50  99% 
100%  0%  Building  42.94  78.54  83% 
180%  0%  Building  55.80  95.11  70% 
The first three columns show the relevant statistics on the attacker or defender, then the next two columns show the DPS/hton for the D92U and the D92F, and then the last column shows the percentage more DPS/hton done by the D92F.
So, for any scenarios where shockwaves are being triggered, the D92F ALWAYS does more damage per weight than the D92U. Of course, if shockwaves are NOT being triggered, it is obvious that the D92F will be doing more damage, because of its much higher base damage.
The only other factor to take into consideration is whether there are loadouts where using D92U will trigger shockwaves where an equal weight of the D92F won't. I'm going to skip the big table and say... yes there are situations like that, but there aren't many. This calculator will tell you a shockwave threshold, but it isn't quite accurate because the nature of salvo fire. For example, if you have 8 D92F firing at a target with 100% net accuracy, you will trigger the first shockwave after 3.9 seconds (during the second salvo), even though you will trigger a shockwave every 5.5 seconds on average.
So... play with the calculator below, if you try to compute the number of launchers you will need to trigger a shockwave, you'll end up with at least as many as you need.