As someone who has had SP250s I can't say I think M Bigorie improved the look of the car, merely changing one slightly inept bit of frontal styling for another. What's more at the speed the car was capable of the lift generated by his front wing treatment must compromise front-end grip. The cut-back rear fins also are no improvement and the originals really were there for cross-wind stability reasons, not just show.
The SP didn't need a higher axle ratio as it ran out of speed pretty well exactly at the engine speed for max. power. With a higher ratio axle it might be happier at 70 m.p.h. but could be one of those cars that are faster in third gear than in top. If the engine was tuned it wouldn't help as any power increase that was achieved (when they were raced in contemporary club events) over that of the production engine used more r.p.m.
