They make 2.5in SAS drives for enterprise environment. They do come in 10L and 15K rpms in roughly the same sizes as their 3.5in counterparts. These days, I'm looking more for low wattage/heat and less space. I'm moving away from the rack environment w/2u or 4u servers at home... With the standardization of SATA connectors for desktop and laptop drives, I can mix and match drives as I want without needing additional adapters. and they make some nice enclosures/drive racks for them.
I've pretty much gone all 2.5in for system drives and 1TB storage drives in my servers. Since most systems/users don't notice any diff between 5400 or 7200, I can use what is affordable for system drives. I can also throw in some 2.5inch SAS drives, but that requires a SAS controller and a mobo w/supporting PCI-e slots. All this just becomes factors in my upgrade plans.
It also simplifies inventory management and cuts down on my spreadsheet. 2.5inch drives are also easier to handle, "feel" sturdier, maybe more durable due to the portable nature of laptop drives, and take up less space.
and between the Intel/AMD platrforms, roughly, one had lower speeds/wattage at idle, the other had lower wattage during loads... (IIRC from comparisons done last year?)... so it varied depending on how often they would sit at load, or at idle... I think Intel at idle ran at 1Ghz and higher watt, while AMD ran at 800Mhz and lower watt. But Intel at full load ran less watt for equivalent Ghz...
I went cheap w/AMD since performance had no *real world impact* in my day 2 day... taking the extra few seconds/minutes didn't really matter and 4+GB of ram is enough to keep things fast. If I was encoding, I would look at SAS or the WD Raptor drives.
oh and prices vary by continent, so things may be equal $ down in Oz...