TLDR: The different types of drive use different type of NAND. The Force GT should be faster than the Force 3, but the Force GS should be faster again. How much of a difference you'll notice is difficult to say though.
Consolidating the information in the other answers it appear that the three subtly differing models use very subtly different types of NAND flash that offer some slight performance increases.
From WWWs link
Model Seq. R/W(MB/s) Random 4k Write NAND Type
Force 3 550/520 85K IOPS Asynchronous NAND
Force GT 555/525 85K IOPS Synchronous NAND
Force GS 555/525 90K IOPS Toggle NAND
Benchmarking of the three types of Flash memory seems to suggest the same as above, that Asynchronous flash is the slowest, Synchronous is better and Toggle mode NAND is the best.
The difference between Asynchronous and Synchronous NAND appears to be improved bandwidth between the controller and NAND chips as per HardOCP:
Both flash types use a 25nm die package size. The technical term is ONFi 2.x (synchronous) and ONFi 1.0 (asynchronous). ONFi 2.x uses a central timing circuit and moves data on both the rise and fall of the signal wave. This is similar to double data rate random access memory (DDR RAM). ONFi 2.0 is capable of delivering speeds up to 133MB/s but ONFi 1.0 is limited to just 50MB/s. On paper it sounds like one is twice as fast as the other but due to the total SSD architecture the real world benefit is much less.
The "maximum read/write" speed specification seems to be based on theoretical performance figures while the real world benchmarks show a marked improvement in speed for Synchronous NAND over Asynchronous NAND.
Toggle NAND is another new way of handling the NAND flash and should provide improvements again over the speeds of Synchronous NAND, as per Toshiba
Toshiba offers a full lineup of 32nm DDR Toggle-Mode NAND, in MLC versions with densities of 64Gb1, 128Gb and 256Gb and SLC versions with densities of 32Gb, 64Gb and 128Gb. Toggle-Mode NAND is a DDR NAND solution designed to consume less power than synchronous DDR NAND flash by eliminating the clock signal typically used in synchronous DDR memories.
Toshiba DDR Toggle-Mode 1.0 NAND has a fast interface, rated at 133 megatransfers/second (MT/s), as compared to 40MT/s for legacy SLC single data rate NAN. This makes it suitable for high performance solid state storage applications, including enterprise storage.
With an asynchronous interface similar to that used in conventional NAND, the Toggle-Mode DDR Flash NAND requires no clock signal, which means that it uses less power and has a simpler system design when compared to competing synchronous NAND alternatives. The DDR interface in Toggle-Mode NAND uses a Bidirectional DQS to generate input/output signals (I/Os) using the rising and falling edge of the write erase signal.
Outside of the technical publications actual distinctions of what each type of flash is and how they function appears to be a bit hard to come by.