(1) NO, DO NOT split the SSD for SRT, use it as a OS + program drive.
(2) SSD Benifit. Faster OS load, faster program load times. After program loads the program will not run faster. If data is requested by the program and that data is on the SSD it will load the data faster. If on the HDD then will load at the speed of the HDD. SRT will ONLY improve on the HDD performance if the Data is in the "cache", for non repeditive requests for data, the data will not be in cache and revert to normal HDD speed.
(3) My choice of SSDs is currently the Curicial M4, do not be fooled by SF2281 controller based SSDs high Sequencial perfoormance.
(A) Sequencial performance is the least important matrix for a OS + Program drive, it is the 4k random performance that is important.
(B) Most benchmarks use NON compressed data (NOT real life), and Yes the SF2281 shines when data that is readily compressable is used - BUT compare the performance when compressed data is used such as used by AS SSD benchmark program.
Screen shot of My M4 (With Firmware 0009) using AS SSD.