I don't know how powerfull the Mediatek Chip is but his 800 MHz looking to me it can handle this easy. A list with 6000 entries is IMO nothing. I would expect over 100k like some aggregated ablock lists easy achive.
There is a package called BanIP available (based on ipset) and there is a support thread for it: banIP support thread
Ask the ppl. there or read it. I think that the limiting factor here is the RAM and not the CPU. But that is just a guess.