When to rebuy in a one-table tourney

[mojo]

I play 4-6 handed poker with my friends when my time allows. We play NL 25-50, 50-100, 100-200 etc. blinds which more or less double every 20 minutes (each player starts with 5000 in chips). The problem is that people can rebuy up to and including when the blinds are 500-1000. I easily survive until that point but other people who bust out then buy back and beat me. I can't justify buying back when the blinds are that high relative to starting chips (i.e. buyback for 5000 and blinds are 500-1000). If I feel I play a better game then my opponents, should I ALWAYS buy back if I can? Also, would I benefit from reading 6max posts with this type of format? THANKS.