When the reg was at factory setting of 2000 psi I was getting 63 shots, since then I raised reg pressure to 2400 psi. Also added a pin probe which gave about 35 fps more velocity.
I've had the GX CS3 for a little over a year and I've had no problems with mine. Paid 300 for it on Amazon on sale. It's a little more now but still very affordable.
I'll recommend the GX CS3. I've had mine for a little over a year and so far no problems. Fills a 500cc bottle from empty to full in 15 mins and doesn't brake the bank.
Sorry don't have a link but he goes by pau.dambe on eBay. He also has a drilling jig to open the transfer port as well as an fx barrel kit. Check out Paul's urban hunter on utube. Another one on eBay is c88 machining, makes nice custom parts for the zelos and notos