There are now 640GB drives from Samsung (M7) and WD (Blue) that use 320GB platters but that doesn't mean the older/smaller ones have larger platters now.
I don't think there are any 250GB disks that are confirmed as using a single platter and definitely no 320GB ones yet.
From you're other thread you mention noise and power, the extra platter makes very little difference to this. Laptop drives are already very quiet and power difference would be completely negligible.
Laptop usually but right this moment both are in external docks so noise/vibration is quite noticeable. The only time you can really hear them in something is when the heads are parked or they spin up/down.
My WD Scorpio Black (7200rpm) is very quick, quiet and cooler, with not power consumption difference, certainly compared to my old Fujitsu 5400rpm drive. Don't worry too much about platters, but go for disk speed.