People with Intex pools are usually happy with the 2500 GPH pump/filter over the smaller pumps which just don't have the power for proper circulation and cleaning.

But for a 6000 gallon pool, you would want a minimum of 45 sq-ft but ideally a 90 sq-ft filter would minimize cleaning to once per season. So the 2500 GPH combo might be insufficient for this size pool. However, there are plenty of combo units made by Hayward and Pentair which would work well. For example, the PNCC0100OE1160 might be a good choice. If you want a two speed pump, I would go with the PNCC0150OF2160 which has a larger filter to match the larger pump.

You can check out all the Pentair combo units here:

http://www.pentairpool.com/pool-pro/...-system-26.htm