well, even DDR3 motherboards really don't cost that much more either (really you are looking at AMD or LGA 775 for comparison)
i agree with the 2 pci-e slots, anyone building a gaming build should go for it, the boards can be found cheap
as for DDR4 vs DDR3, well get there when it comes, though if history is any indicator, DDR3 will plummet (maybe not as much as DDR2 did) and DDR4 will be expensive and over time the will even and then DDR3 will get more expensive as it turns into a legacy memory type (look at the prices of DDR right now)
as a history example, i bought my PC in April 2009, i got 8GB(4x2GB) for $70
btw, if you wait for DDR4 now, when it hits you will probably wait for DDR5 (or the next best thing), right now though for AMD users looking to buy right now, make sure to get an 8 series north bridge possible Bulldozer compatibility)
DDR3 has a higher bandwidth, but not necessarily better performance because of latencies since they go up as speed does (ie CL4 DDR2-800 has the same CL delay as CL8 DDR3-1600)