Asking whether SAS is better than SSD is like asking whether IDE is better than a tape drive.
SAS is a drive interface, like SCSI, IDE or SATA. SSD is a drive technology, like CD, DVD or Hard drive.
Just as you can get Hard Drives with any of the above interfaces, you can get SSD's with different interfaces too.
So, ignoring the question title - as with many questions like this, the answer is 'it depends'.
Normally when people compare the performance of storage media, they look at the headline 'throughput', Megabytes per second, but this is only really valid when doing large block reads and writes. For software development, where the number of different, often small, files which need to be read and written to compile an application is quite large, the number of I/O operations per second can be much better indicator of overall performance.
As such, I tend to assume that software development fits uder the "Workstation performance" model.
So when I research the best options for new hardware, I tend to go to Tom's Hardware and look at the workstation benchmarks. For instance the new VelociRaptors are head and shoulders over typical 7200rpm SATA hard drives, but even these figures pale into insignificant when you compare them to the top end SSD's.
Ultimately though, it is up to you to determine whether the performance differences justify the extra costs.
Just to add some fuel to the fire, if you are considering one of the cheaper SSD's out there, you might be ineterested to see these articles at Anandtech and PC perspective. It might take you a while to read through them, but you will learn an immense amount about SSD's, what to look out for and what to avoid.
This is only a guess - because XP does not support TRIM, your sequential write is going over blocks that once had data on them and needs to erase them before writing them, this will slow down the write performance of the drive.
When you are performing random writes, the drive might be writing to blocks that are truly blank, resulting in faster performance because the drive does not have to perform an erase operation first.
There are utilities for Operating Systems that do not support TRIM that will go through the drive and erase data on blocks that are not storing information for the filesystem.
Wikipedia - TRIM
Best Answer
yes, secure erase boosts the performance to the default values. I do this each time I reinstall Windows. Your SSD with SandForce controller will benefit from it very much.
http://forums.sandisk.com/t5/SanDisk-Extreme-SSD/HOW-TO-GET-YOUR-SSD-PERFORMANCE-BACK/td-p/281740