gearing a 4.5 indoors for 501x

[tenoracer 22]

tested my new 501 x at DMS with a 4.5 on Thursday. The track is small and 90% carpet. I was gearing with 17 / 96 with the big pulley conversion. car was really sluggish , I was testing with an old pack of 4200 nimh s were these at fault or am I overgeared? probably going to run with cells for the rest of this year so help would be appreciated. Cheers, Phil.
ps running a nosram itcs speedo, if you have any experience with settings this would be great also .