Hosting advantage goes to the SP30 - it's less rack space and less power consumption.
Professional hosting is about $100/kw.
SP30: $300/mo
S3: $350/mo
So you need to run the SP30 for 20 months to make up for the price advantage of the S3. Good luck with that.
10 s3's are now more than $1500 cheaper than an sp30 so it would be 30+ months.