OK, I tried using fetchtst, with all rows and got these results. The all-rows with 4 ids has a much longer fetch first row time, but it's still nothing like 15 seconds through ISQL. I don't really know where to go after this either.

optimization_goal = 'all-rows' IN (1,2,3,4)

Statement 1 (line 1): SELECT phclientid, firstname, lastname, lastn...
PREPARE:              0.001 seconds
DESCRIBE:             0.048 seconds
OPEN:                 0.446 seconds
FETCH first row:      1.413 seconds, 0 I/Os,   0 per second
FETCH remaining rows: 0.000 seconds
CLOSE:                0.004 seconds
DROP:                 0.000 seconds
Total:                1.910 seconds, 0 I/Os,   0 per second
Fetch rate: 4 rows in 1.413 seconds,      2.831 per second

optimization_goal = 'all-rows' IN (1)

Statement 1 (line 1): SELECT phclientid, firstname, lastname, lastn...
PREPARE:              0.001 seconds
DESCRIBE:             0.048 seconds
OPEN:                 0.169 seconds
FETCH first row:      0.006 seconds, 0 I/Os,   0 per second
FETCH remaining rows: 0.000 seconds
CLOSE:                0.000 seconds
DROP:                 0.000 seconds
Total:                0.224 seconds, 0 I/Os,   0 per second
Fetch rate: 1 rows in 0.006 seconds,    163.324 per second

What builds of v8 and v11 are you using? I would recommend to use the latest major version (8.0.3. and 11.0.1) and the according latest EBFs to make sure any improvements/bugfixes are contained. (Note that I'm not aware of particular fixes for such IN list optimization.) - Just as a general recommendation...

In v8 Single row

PREPARE:              0.000 seconds
DESCRIBE:             0.019 seconds
OPEN:                 0.041 seconds
FETCH first row:      0.005 seconds, 0 I/Os,   0 per second
FETCH remaining row:  0.000 seconds
CLOSE:                0.000 seconds
DROP:                 0.000 seconds
Total:                0.066 seconds, 0 I/Os,   0 per second
Client total:         0.066 seconds
Fetch rate: 1 rows in 0.005 seconds,    193.787 per second

Multiple row

PREPARE:              0.000 seconds
DESCRIBE:             0.020 seconds
OPEN:                 0.045 seconds
FETCH first row:      0.008 seconds, 0 I/Os,   0 per second
FETCH remaining row:  0.002 seconds
CLOSE:                0.000 seconds
DROP:                 0.000 seconds
Total:                0.075 seconds, 0 I/Os,   0 per second
Client total:         0.076 seconds
Fetch rate: 4 rows in 0.010 seconds,    418.236 per second

These times were taken from a v8 database with similar data (but not the same I have since discovered). If I use the v8 fetchtst.exe against the same v11 database I get very similar results. I do not have access to the v8 version of the v11 database. The v11 database was taken from a production site that I do not have access to.

Don't think so. I'm not familiar with the rules about that but I know that it has confidential info. Plus, it's over 3GB.