Increasing array size; slower drives or slower RAID config?

I am spec'ing out a personal lab virtual environment and had a question that i thought someone in this forum could provide some opinions on. My question relates to RAID/drive configuration. I am trying to avoid purchasing external DAS storage and maintain similar RAID 10 (6 x 15kRPM) performance that i have configured in other non-production environments. The issue came about because I have traditionally ordered these small single box development environments with Dell R710 servers that have 6x600GB 3.5" 15kRPM drive options and the Dell R715 server only offers 2.5" drive options. With the R715 the largest drive at 15k RPM that I can order is 300GB, which means I would only be able achieve approximately 900GB of usable storage at the reference point that I know would support this environment. My estimate shows that I would only have approximately 300GB of storage after the environment is built which is a little too close for comfort.

Assuming i want to stick with a similar price tag to a single loaded R715, and achieve more usable storage. Would i see better performance (without adding too much extra to the sticker price) by......

*** starting with six 300GB 15k RPM drives at raid 10 ***

A) changing to six 300GB 15k RPM drives at raid 50, i would be comfortable with ~1.2 TB

B) changing to six 600GB or 900GB 10k RPM drives at raid 10.

C) start thinking about re-configuring the solution, e.g. start looking at single/dual server DAS config, adding NAS, moving storage offenders to other hardware, etc.

D) Some other config?

Any opinions are appreciated.

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Base Hardware: PowerEdge R715 - 2x AMD Opteron 6282SE, 2.6GHz, 16C -  128GB Ram, SD Module

OS: VMWare Essential on embedded SD module

Virtual Environment: Active Directory, really small file server, Exchange 2010, SharePoint 2010 (3 tier setup running all enterprise components), small Oracle server for integration testing, Win7 SharePoint development workstation, 4-5 windows clients, 3-4 other utility servers for developing enterprise solutions and testing SharePoint integrations.