all ski doo electronic speedos from 03-07 switch to digital speed after 55 mph
as for the topic at hand
if you want fuel milage go with the sdi if you want reliability go with carbs
every sdi I've had 600 and 1000 have had piston, crank, and stator problems
never had any trouble with the carb versions
sucking snow into 99 500 does not count as that was never the issue with sdi's as to why they went down
600 sdi 3 times over 3600 miles one time there was only 300 miles between piston jobs
02 600 carb 9300 miles no problems and that sled was better on fuel than the sdi
04 600 carb no engine trouble but it liked its fuel