It wouldn't surprise me if the Pacers were generally quite a bit more frugal than the Sprinters, their current engines (10 litre straight-six turbo diesel Cummins LTA10R, 230hp) are a smaller, slightly more modern (early '80s) design than the 1960s era design of the NT855R5 used in the 150/3/5/6 units (straight six, turbo diesel, 285hp).
The Sprinters have a bigger compressed air system so the engine-driven compressor probably adds more auxiliary load on the engine, and they also have a master and slave final drive on the #2 (driven) bogie which will add very slightly to mechanical drag/losses under power.
Pacer vehicles have a single driven axle hence a single final drive. The transmissions on both Sprinters and Pacers are very similar in operation and when coasting there is no noticeable drag. 142s and 144s retain their old twin alternator system whereby a cardan shaft off the free end of the engine drives a splitter gearbox which has a further shaft to each of two alternators on each vehicle, which supply the auxiliary power and charge the start batteries. The start batteries are also used for most safety critical and control circuits on the unit. Class 150/2s had a very similar alternator setup to the Pacers but 150s are being modified with a new 'alternator raft' which has one mechanical input which turns the alternator via a hydrostatic pump, the new alternators having their own oil circuit. All other Sprinters bar the /2s have always had a single alternator. I can't see the older/Pacer alternator setup having a great deal of difference on mechanical drag but it's possibly noticeable.
Where the fuel consumption tables will be turned though will be at higher running speeds - Pacers, being only about 2/3 the weight of Sprinters and being less powerful, suffer far more from wind resistance at speed and their power drops off markedly above 60mph. This effect is reduced when units are coupled in multiple as the frontal wind resistance is probably virtually nothing for the second unit, although the wind resistance for the rest of the unit (particularly around underfloor equipment, bodyside etc) will remain about the same. When taking a single 142 on a flat, relatively featureless route such as Wigan to Southport and back you can usually tell which way the wind is blowing by the performance (or lack of) one way vs the other.