The G-Monster V4S is a chip off the ole PhotoFast block and is just as impressive as the V5 and Promise PCIe. When it really comes down to it, the V5 appears to be a little faster for consumer use, but the longevity of SLC makes the V4S better suited for enterprise uses.
At 499 USD for the 32GB G-Monster V4S, the drive has a couple of competitors that are very fast as well. Sitting on equal ground technology wise, the Solidata K5 costs about the same and is only slightly slower. Just as the X25-M does in the desktop market, the enterprise X25-E casts a long shadow. The X25-E costs around 80 USD less and its ten channel controller makes it very fast as well, but it does have an issue with TRIM that makes it less desirable at this time.
When it comes to availability, DVNation keeps the G-Monster V4S in stock in 32GB capacity. The V4S is also available in 64GB and 128GB capacities, all with the same 64MB of cache.