[MetalMan]

boss, there are 7 cells in the V28 packs. A 3s2p pack uses 6 cells, which means one left over. 2 packs will give 6s2p and then 2s1p.

David, that would work perfectly. Just make sure not to use anything more than a stock motor with the 2s1p, since these cells may/may not be able to handle the amp draw.

BrianG, it would be more convieniant to have a pack that is constructed in 2p5s, or two packs with one being 3s2p and the other 2s2p. That way, you don't have two packs "fighting" each other over differences in voltage, although this wouldn't be a problem worth worrying about. But, it would make charging A LOT easier, since electrically you only have 5 cells to balance, as opposed to 2 5s1p packs where there are 10 cells to balance. If you did end up charging the two 5s1p packs in parallel, you'd want to use one balancer per pack. The only downside with this is that if one balancer (on one pack) is balancing a cell, it will drop the voltage of the pack, causing that pack to receive a higher current to make up for the lower voltage it has compared to the other pack that isn't sinking any current (from a cell that needs balancing).
In conclusion, it would be much better to have 5 groups of 2 cells in parallel (IMO).