There's any number of great guns that fit into both IPSC Production and IDPA Stock Service Pistol. I'm a fan of CZ so I'll suggest a CZ 75b or 85b. I'd suggest the SP-01 Shadow but you need to jump through some hoops to make it light enough to fit into IDPA. But if you'd stick with IPSC then the Shadow is one of the more popular options and a great way to go. I'd suggest some other guns such as Glock and M&P but I'm an all steel with proper hammer gun type of guy and don't cotton to 'dem oddball striker fired gumball plastic guns... 
In the end it really doesn't matter what gun you get, as long as it is on the IPSC Production class approved list. The list of approved Production class guns is available online with a bit of a google search. You've shot enough stuff that you know what sort of style of gun that you feel most comfortable with so it's just a case of finding one that you liked on the list and getting one of them again.
It's the new focus on speed with accuracy that'll stir the juices moreso than the actual gun. After all the gun is just a tool much like a tennis racket is just a tool or a set of golf clubs is just a tool. You want a GOOD tool that is in tune with you but the excitement will come from the game itself.
Just for the helluva it and to get a taste of the style of shooting try some multi target practice when you take one of your present handguns to the range next time. If it's like many clubs you often have a great swatch of room all to yourself on the handgun range. So set up two or three targets arrayed in front of you and with some different distances. Work on raising the gun from a low ready position onto the first target, double tap, next target, double tap, etc. Bring along a pair of binos so you can check how you're doing. Definetly shoot with accuracy as your primary concern but do try to balance ultimate centering with some speed. If you're really keen invest in a shot timer so it beeps at you and records your shot times. It's quite the eye opener to see the times for first shots and follow up shots when reviewing all the separate shots in a string. We typically are nowhere near as fast as we think we are.
In the end it really doesn't matter what gun you get, as long as it is on the IPSC Production class approved list. The list of approved Production class guns is available online with a bit of a google search. You've shot enough stuff that you know what sort of style of gun that you feel most comfortable with so it's just a case of finding one that you liked on the list and getting one of them again.
It's the new focus on speed with accuracy that'll stir the juices moreso than the actual gun. After all the gun is just a tool much like a tennis racket is just a tool or a set of golf clubs is just a tool. You want a GOOD tool that is in tune with you but the excitement will come from the game itself.
Just for the helluva it and to get a taste of the style of shooting try some multi target practice when you take one of your present handguns to the range next time. If it's like many clubs you often have a great swatch of room all to yourself on the handgun range. So set up two or three targets arrayed in front of you and with some different distances. Work on raising the gun from a low ready position onto the first target, double tap, next target, double tap, etc. Bring along a pair of binos so you can check how you're doing. Definetly shoot with accuracy as your primary concern but do try to balance ultimate centering with some speed. If you're really keen invest in a shot timer so it beeps at you and records your shot times. It's quite the eye opener to see the times for first shots and follow up shots when reviewing all the separate shots in a string. We typically are nowhere near as fast as we think we are.
